Add const to the variable: needle
Add const to the variable: needle

Summary:
Make it clear that the variable is const

Closes #139

Test Plan:
authored tested, contbuild

Reviewed By: markisaa@fb.com

Subscribers: folly-diffs@, yfeldblum

FB internal diff: D1878361

Signature: t1:1878361:1425071448:6871577ddb34f4a8dc30ea37842f9950c3825dde

gavioto/folly,PPC64/folly,sonnyhu/folly,bowlofstew/folly,KSreeHarsha/folly,juniway/folly,guker/folly,shaobz/folly,rklabs/folly,Hincoin/folly,raphaelamorim/folly,SammyK/folly,bikong2/folly,romange/folly,doctaweeks/folly,wildinto/folly,hongliangzhao/folly,arg0/folly,gaoyingie/folly,theiver9827/folly,renyinew/folly,stonegithubs/folly,lifei/folly,kernelim/folly,fw1121/folly,project-zerus/folly,shaobz/folly,loversInJapan/folly,fw1121/folly,PPC64/folly,CJstar/folly,gavioto/folly,SammyK/folly,xzmagic/folly,rklabs/folly,theiver9827/folly,bikong2/folly,clearlinux/folly,tomhughes/folly,clearlylin/folly,stonegithubs/folly,colemancda/folly,charsyam/folly,ykarlsbrun/folly,ykarlsbrun/folly,Hincoin/folly,raphaelamorim/folly,fw1121/folly,brunomorishita/folly,juniway/folly,reddit/folly,SeanRBurton/folly,PoisonBOx/folly,bsampath/folly,gaoyingie/folly,constantine001/folly,nickhen/folly,Eagle-X/folly,floxard/folly,reddit/folly,lifei/folly,sakishum/folly,cole14/folly,mqeizi/folly,alexst07/folly,cole14/folly,chjp2046/folly,leolujuyi/folly,reddit/folly,chjp2046/folly,theiver9827/folly,doctaweeks/folly,bobegir/folly,Hincoin/folly,loverszhaokai/folly,upsoft/folly,leolujuyi/folly,Hincoin/folly,SeanRBurton/folly,romange/folly,project-zerus/folly,renyinew/folly,juniway/folly,loverszhaokai/folly,constantine001/folly,SammyK/folly,Eagle-X/folly,cppfool/folly,zhiweicai/folly,hongliangzhao/folly,kernelim/folly,shaobz/folly,charsyam/folly,gavioto/folly,sakishum/folly,loversInJapan/folly,PoisonBOx/folly,PoisonBOx/folly,floxard/folly,Orvid/folly,loverszhaokai/folly,bsampath/folly,mqeizi/folly,clearlinux/folly,raphaelamorim/folly,tempbottle/folly,upsoft/folly,hongliangzhao/folly,gaoyingie/folly,cole14/folly,sakishum/folly,gaoyingie/folly,gavioto/folly,bowlofstew/folly,xzmagic/folly,doctaweeks/folly,bowlofstew/folly,loverszhaokai/folly,bsampath/folly,sakishum/folly,shaobz/folly,arg0/folly,yangjin-unique/folly,yangjin-unique/folly,lifei/folly,ykarlsbrun/folly,bikong2/folly,mqeizi/folly,rklabs/folly,wildinto/folly,clearlylin/folly,nickhen/folly,bobegir/folly,tempbottle/folly,wildinto/folly,leolujuyi/folly,sakishum/folly,constantine001/folly,loverszhaokai/folly,bsampath/folly,constantine001/folly,arg0/folly,leolujuyi/folly,raphaelamorim/folly,doctaweeks/folly,Eagle-X/folly,tempbottle/folly,nickhen/folly,CJstar/folly,chjp2046/folly,charsyam/folly,reddit/folly,project-zerus/folly,Orvid/folly,romange/folly,bikong2/folly,bobegir/folly,KSreeHarsha/folly,nickhen/folly,colemancda/folly,CJstar/folly,wildinto/folly,cppfool/folly,Orvid/folly,xzmagic/folly,hongliangzhao/folly,cppfool/folly,colemancda/folly,zhiweicai/folly,upsoft/folly,sonnyhu/folly,tomhughes/folly,hongliangzhao/folly,renyinew/folly,facebook/folly,sonnyhu/folly,KSreeHarsha/folly,juniway/folly,theiver9827/folly,gaoyingie/folly,rklabs/folly,wildinto/folly,yangjin-unique/folly,doctaweeks/folly,zhiweicai/folly,project-zerus/folly,SeanRBurton/folly,leolujuyi/folly,stonegithubs/folly,kernelim/folly,Eagle-X/folly,Orvid/folly,SammyK/folly,fw1121/folly,PPC64/folly,cppfool/folly,gavioto/folly,bowlofstew/folly,tempbottle/folly,cppfool/folly,alexst07/folly,guker/folly,SammyK/folly,alexst07/folly,guker/folly,tomhughes/folly,xzmagic/folly,zhiweicai/folly,CJstar/folly,zhiweicai/folly,facebook/folly,sonnyhu/folly,tempbottle/folly,loversInJapan/folly,alexst07/folly,renyinew/folly,bikong2/folly,brunomorishita/folly,loversInJapan/folly,tomhughes/folly,PoisonBOx/folly,bobegir/folly,shaobz/folly,rklabs/folly,Eagle-X/folly,loversInJapan/folly,cole14/folly,sonnyhu/folly,arg0/folly,clearlylin/folly,upsoft/folly,juniway/folly,KSreeHarsha/folly,theiver9827/folly,facebook/folly,stonegithubs/folly,romange/folly,brunomorishita/folly,PPC64/folly,constantine001/folly,PoisonBOx/folly,floxard/folly,alexst07/folly,bowlofstew/folly,clearlylin/folly,yangjin-unique/folly,lifei/folly,guker/folly,mqeizi/folly,chjp2046/folly,yangjin-unique/folly,bsampath/folly,raphaelamorim/folly,stonegithubs/folly,clearlinux/folly,kernelim/folly,chjp2046/folly,Hincoin/folly,floxard/folly,kernelim/folly,mqeizi/folly,SeanRBurton/folly,reddit/folly,romange/folly,nickhen/folly,fw1121/folly,facebook/folly,facebook/folly,tomhughes/folly,CJstar/folly,brunomorishita/folly,KSreeHarsha/folly,guker/folly,arg0/folly,clearlinux/folly,brunomorishita/folly,ykarlsbrun/folly,colemancda/folly,PPC64/folly,colemancda/folly,charsyam/folly,renyinew/folly,bobegir/folly,cole14/folly,ykarlsbrun/folly,floxard/folly,SeanRBurton/folly,project-zerus/folly,upsoft/folly,Orvid/folly,clearlinux/folly,clearlylin/folly,lifei/folly,xzmagic/folly