Fix minor bug in missing symbol finder
Fix minor bug in missing symbol finder

Summary:
The missing java symbol support, which hunts down rules that resolve
missing symbol errors in java, parses BUCK up the dir tree in an effort
to find the owners of sources.  It determines that a file is a BUCK file
by checking that it's basename is BUCK.  However, it's possible that
the user has a directory by this name, and this is even more likely
on case-insensitive filesystems where a directory called "buck" would
be mistaken for a BUCK file and parsed, resulting in an ugly parse
error.

This diff changes the code to check that the given path is a file
to avoid this.

Test Plan:
Removed some needed deps in test code and ran ##buck test --all##.

rowillia/buck,liuyang-li/buck,shs96c/buck,Distrotech/buck,saleeh93/buck-cutom,mnuessler/buck,SeleniumHQ/buck,justinmuller/buck,shybovycha/buck,zhuxiaohao/buck,OkBuilds/buck,shs96c/buck,SeleniumHQ/buck,raviagarwal7/buck,janicduplessis/buck,marcinkwiatkowski/buck,rhencke/buck,justinmuller/buck,OkBuilds/buck,luiseduardohdbackup/buck,zhuxiaohao/buck,MarkRunWu/buck,k21/buck,OkBuilds/buck,rhencke/buck,vine/buck,darkforestzero/buck,mogers/buck,dpursehouse/buck,janicduplessis/buck,rmaz/buck,liuyang-li/buck,romanoid/buck,lukw00/buck,bocon13/buck,zhan-xiong/buck,mogers/buck,hgl888/buck,vschs007/buck,1yvT0s/buck,clonetwin26/buck,JoelMarcey/buck,SeleniumHQ/buck,MarkRunWu/buck,shybovycha/buck,dushmis/buck,artiya4u/buck,raviagarwal7/buck,Addepar/buck,illicitonion/buck,shs96c/buck,pwz3n0/buck,brettwooldridge/buck,brettwooldridge/buck,davido/buck,rowillia/buck,Dominator008/buck,Learn-Android-app/buck,rmaz/buck,stuhood/buck,darkforestzero/buck,luiseduardohdbackup/buck,liuyang-li/buck,clonetwin26/buck,mnuessler/buck,davido/buck,k21/buck,mikekap/buck,dushmis/buck,vschs007/buck,vine/buck,nguyentruongtho/buck,vschs007/buck,lukw00/buck,liuyang-li/buck,marcinkwiatkowski/buck,clonetwin26/buck,saleeh93/buck-cutom,zhan-xiong/buck,vine/buck,saleeh93/buck-cutom,Learn-Android-app/buck,janicduplessis/buck,sdwilsh/buck,tgummerer/buck,pwz3n0/buck,stuhood/buck,justinmuller/buck,kageiit/buck,pwz3n0/buck,artiya4u/buck,dushmis/buck,dsyang/buck,zhuxiaohao/buck,justinmuller/buck,janicduplessis/buck,Heart2009/buck,janicduplessis/buck,SeleniumHQ/buck,raviagarwal7/buck,mogers/buck,lukw00/buck,SeleniumHQ/buck,romanoid/buck,raviagarwal7/buck,nguyentruongtho/buck,janicduplessis/buck,zhuxiaohao/buck,Distrotech/buck,justinmuller/buck,hgl888/buck,liuyang-li/buck,luiseduardohdbackup/buck,lukw00/buck,pwz3n0/buck,rhencke/buck,1yvT0s/buck,rmaz/buck,rmaz/buck,LegNeato/buck,shs96c/buck,mogers/buck,mread/buck,bocon13/buck,Learn-Android-app/buck,Addepar/buck,shs96c/buck,stuhood/buck,neonichu/buck,darkforestzero/buck,lukw00/buck,MarkRunWu/buck,daedric/buck,OkBuilds/buck,k21/buck,marcinkwiatkowski/buck,romanoid/buck,Heart2009/buck,grumpyjames/buck,vine/buck,robbertvanginkel/buck,clonetwin26/buck,bocon13/buck,grumpyjames/buck,k21/buck,tgummerer/buck,sdwilsh/buck,clonetwin26/buck,robbertvanginkel/buck,raviagarwal7/buck,vschs007/buck,darkforestzero/buck,raviagarwal7/buck,rowillia/buck,marcinkwiatkowski/buck,dsyang/buck,brettwooldridge/buck,davido/buck,saleeh93/buck-cutom,k21/buck,mread/buck,OkBuilds/buck,artiya4u/buck,artiya4u/buck,rowillia/buck,marcinkwiatkowski/buck,mnuessler/buck,robbertvanginkel/buck,Heart2009/buck,k21/buck,darkforestzero/buck,sdwilsh/buck,artiya4u/buck,mikekap/buck,davido/buck,vine/buck,rmaz/buck,SeleniumHQ/buck,SeleniumHQ/buck,lukw00/buck,neonichu/buck,rhencke/buck,zpao/buck,Learn-Android-app/buck,MarkRunWu/buck,zpao/buck,clonetwin26/buck,LegNeato/buck,lukw00/buck,Learn-Android-app/buck,zhan-xiong/buck,LegNeato/buck,vschs007/buck,ilya-klyuchnikov/buck,bocon13/buck,Addepar/buck,pwz3n0/buck,nguyentruongtho/buck,daedric/buck,1yvT0s/buck,Distrotech/buck,Dominator008/buck,dsyang/buck,Distrotech/buck,brettwooldridge/buck,OkBuilds/buck,Addepar/buck,stuhood/buck,sdwilsh/buck,romanoid/buck,dsyang/buck,darkforestzero/buck,k21/buck,artiya4u/buck,romanoid/buck,Distrotech/buck,romanoid/buck,darkforestzero/buck,raviagarwal7/buck,brettwooldridge/buck,zhan-xiong/buck,dushmis/buck,LegNeato/buck,saleeh93/buck-cutom,rmaz/buck,liuyang-li/buck,LegNeato/buck,dsyang/buck,robbertvanginkel/buck,daedric/buck,1yvT0s/buck,shybovycha/buck,robbertvanginkel/buck,vschs007/buck,rhencke/buck,Heart2009/buck,davido/buck,bocon13/buck,romanoid/buck,justinmuller/buck,rowillia/buck,mikekap/buck,vschs007/buck,ilya-klyuchnikov/buck,clonetwin26/buck,illicitonion/buck,pwz3n0/buck,rmaz/buck,brettwooldridge/buck,zhuxiaohao/buck,LegNeato/buck,grumpyjames/buck,clonetwin26/buck,stuhood/buck,MarkRunWu/buck,robbertvanginkel/buck,mogers/buck,mikekap/buck,ilya-klyuchnikov/buck,luiseduardohdbackup/buck,mikekap/buck,neonichu/buck,justinmuller/buck,mread/buck,OkBuilds/buck,dsyang/buck,robbertvanginkel/buck,illicitonion/buck,mnuessler/buck,facebook/buck,tgummerer/buck,zhuxiaohao/buck,dushmis/buck,dsyang/buck,rmaz/buck,grumpyjames/buck,dsyang/buck,pwz3n0/buck,1yvT0s/buck,JoelMarcey/buck,romanoid/buck,OkBuilds/buck,shybovycha/buck,Dominator008/buck,rmaz/buck,stuhood/buck,daedric/buck,vine/buck,1yvT0s/buck,ilya-klyuchnikov/buck,vine/buck,Dominator008/buck,stuhood/buck,hgl888/buck,ilya-klyuchnikov/buck,justinmuller/buck,zpao/buck,Addepar/buck,davido/buck,Addepar/buck,ilya-klyuchnikov/buck,JoelMarcey/buck,daedric/buck,daedric/buck,davido/buck,tgummerer/buck,mread/buck,grumpyjames/buck,zhan-xiong/buck,shs96c/buck,bocon13/buck,rhencke/buck,SeleniumHQ/buck,darkforestzero/buck,bocon13/buck,daedric/buck,tgummerer/buck,bocon13/buck,justinmuller/buck,Heart2009/buck,davido/buck,hgl888/buck,SeleniumHQ/buck,grumpyjames/buck,mikekap/buck,vschs007/buck,marcinkwiatkowski/buck,romanoid/buck,darkforestzero/buck,LegNeato/buck,mogers/buck,illicitonion/buck,Heart2009/buck,MarkRunWu/buck,hgl888/buck,pwz3n0/buck,illicitonion/buck,luiseduardohdbackup/buck,davido/buck,mread/buck,dushmis/buck,Learn-Android-app/buck,liuyang-li/buck,siddhartharay007/buck,shybovycha/buck,vine/buck,mogers/buck,zhan-xiong/buck,Dominator008/buck,vine/buck,JoelMarcey/buck,justinmuller/buck,brettwooldridge/buck,siddhartharay007/buck,bocon13/buck,marcinkwiatkowski/buck,artiya4u/buck,brettwooldridge/buck,mnuessler/buck,shs96c/buck,vine/buck,shs96c/buck,zhuxiaohao/buck,zhuxiaohao/buck,Addepar/buck,Addepar/buck,kageiit/buck,rowillia/buck,clonetwin26/buck,rowillia/buck,mnuessler/buck,artiya4u/buck,mikekap/buck,JoelMarcey/buck,kageiit/buck,lukw00/buck,hgl888/buck,raviagarwal7/buck,k21/buck,Learn-Android-app/buck,raviagarwal7/buck,JoelMarcey/buck,sdwilsh/buck,dushmis/buck,JoelMarcey/buck,neonichu/buck,dushmis/buck,rowillia/buck,darkforestzero/buck,Addepar/buck,rowillia/buck,nguyentruongtho/buck,dpursehouse/buck,janicduplessis/buck,robbertvanginkel/buck,tgummerer/buck,ilya-klyuchnikov/buck,SeleniumHQ/buck,Addepar/buck,rowillia/buck,grumpyjames/buck,mread/buck,neonichu/buck,facebook/buck,clonetwin26/buck,davido/buck,sdwilsh/buck,tgummerer/buck,mnuessler/buck,k21/buck,justinmuller/buck,OkBuilds/buck,1yvT0s/buck,Learn-Android-app/buck,stuhood/buck,janicduplessis/buck,neonichu/buck,hgl888/buck,rmaz/buck,pwz3n0/buck,Dominator008/buck,janicduplessis/buck,marcinkwiatkowski/buck,mogers/buck,SeleniumHQ/buck,shybovycha/buck,zpao/buck,davido/buck,dsyang/buck,robbertvanginkel/buck,Dominator008/buck,dpursehouse/buck,stuhood/buck,nguyentruongtho/buck,ilya-klyuchnikov/buck,brettwooldridge/buck,mnuessler/buck,siddhartharay007/buck,Heart2009/buck,davido/buck,mikekap/buck,robbertvanginkel/buck,mikekap/buck,marcinkwiatkowski/buck,k21/buck,sdwilsh/buck,siddhartharay007/buck,dsyang/buck,tgummerer/buck,illicitonion/buck,robbertvanginkel/buck,Learn-Android-app/buck,shs96c/buck,zhan-xiong/buck,janicduplessis/buck,saleeh93/buck-cutom,tgummerer/buck,daedric/buck,OkBuilds/buck,luiseduardohdbackup/buck,shybovycha/buck,zhan-xiong/buck,raviagarwal7/buck,grumpyjames/buck,dpursehouse/buck,illicitonion/buck,Dominator008/buck,nguyentruongtho/buck,sdwilsh/buck,siddhartharay007/buck,brettwooldridge/buck,justinmuller/buck,mikekap/buck,lukw00/buck,illicitonion/buck,sdwilsh/buck,illicitonion/buck,mogers/buck,janicduplessis/buck,JoelMarcey/buck,k21/buck,mogers/buck,rhencke/buck,SeleniumHQ/buck,kageiit/buck,clonetwin26/buck,Dominator008/buck,LegNeato/buck,rmaz/buck,mikekap/buck,liuyang-li/buck,MarkRunWu/buck,hgl888/buck,Dominator008/buck,dushmis/buck,neonichu/buck,grumpyjames/buck,artiya4u/buck,OkBuilds/buck,grumpyjames/buck,romanoid/buck,ilya-klyuchnikov/buck,Distrotech/buck,JoelMarcey/buck,facebook/buck,Learn-Android-app/buck,neonichu/buck,daedric/buck,rowillia/buck,Distrotech/buck,shybovycha/buck,dpursehouse/buck,artiya4u/buck,Dominator008/buck,shs96c/buck,daedric/buck,dpursehouse/buck,luiseduardohdbackup/buck,facebook/buck,Distrotech/buck,sdwilsh/buck,robbertvanginkel/buck,illicitonion/buck,davido/buck,zpao/buck,ilya-klyuchnikov/buck,zhuxiaohao/buck,dpursehouse/buck,vschs007/buck,luiseduardohdbackup/buck,ilya-klyuchnikov/buck,justinmuller/buck,marcinkwiatkowski/buck,liuyang-li/buck,Heart2009/buck,Distrotech/buck,bocon13/buck,brettwooldridge/buck,JoelMarcey/buck,sdwilsh/buck,romanoid/buck,rmaz/buck,grumpyjames/buck,brettwooldridge/buck,Heart2009/buck,ilya-klyuchnikov/buck,zhan-xiong/buck,MarkRunWu/buck,rowillia/buck,robbertvanginkel/buck,LegNeato/buck,Learn-Android-app/buck,darkforestzero/buck,liuyang-li/buck,darkforestzero/buck,sdwilsh/buck,pwz3n0/buck,Addepar/buck,1yvT0s/buck,liuyang-li/buck,rhencke/buck,pwz3n0/buck,mogers/buck,Addepar/buck,LegNeato/buck,zpao/buck,shybovycha/buck,stuhood/buck,vschs007/buck,siddhartharay007/buck,stuhood/buck,k21/buck,clonetwin26/buck,illicitonion/buck,kageiit/buck,shs96c/buck,nguyentruongtho/buck,Addepar/buck,facebook/buck,facebook/buck,raviagarwal7/buck,mikekap/buck,OkBuilds/buck,shs96c/buck,zhan-xiong/buck,rhencke/buck,sdwilsh/buck,lukw00/buck,dushmis/buck,LegNeato/buck,bocon13/buck,shybovycha/buck,vschs007/buck,Dominator008/buck,raviagarwal7/buck,daedric/buck,facebook/buck,darkforestzero/buck,marcinkwiatkowski/buck,dpursehouse/buck,illicitonion/buck,zhan-xiong/buck,shs96c/buck,dsyang/buck,rhencke/buck,JoelMarcey/buck,shybovycha/buck,Distrotech/buck,siddhartharay007/buck,zpao/buck,luiseduardohdbackup/buck,dsyang/buck,illicitonion/buck,LegNeato/buck,siddhartharay007/buck,mnuessler/buck,LegNeato/buck,1yvT0s/buck,vschs007/buck,dsyang/buck,neonichu/buck,rmaz/buck,hgl888/buck,marcinkwiatkowski/buck,clonetwin26/buck,JoelMarcey/buck,romanoid/buck,janicduplessis/buck,zhan-xiong/buck,SeleniumHQ/buck,brettwooldridge/buck,artiya4u/buck,tgummerer/buck,lukw00/buck,kageiit/buck,daedric/buck,ilya-klyuchnikov/buck,tgummerer/buck,romanoid/buck,OkBuilds/buck,zhan-xiong/buck,shybovycha/buck,Distrotech/buck,k21/buck,vine/buck,bocon13/buck,kageiit/buck,marcinkwiatkowski/buck,grumpyjames/buck,JoelMarcey/buck,vschs007/buck,raviagarwal7/buck,shybovycha/buck,siddhartharay007/buck,daedric/buck,rhencke/buck