core: allow returning None from spiders to support pipeline/download throttling
core: allow returning None from spiders to support pipeline/download throttling

--HG--
extra : convert_revision : svn%3Ab85faa78-f9eb-468e-a121-7cced6da292c%40990

nfunato/scrapy,rdowinton/scrapy,dangra/scrapy,carlosp420/scrapy,elijah513/scrapy,hyrole/scrapy,Ryezhang/scrapy,kashyap32/scrapy,rolando-contrib/scrapy,pfctdayelise/scrapy,WilliamKinaan/scrapy,heamon7/scrapy,hbwzhsh/scrapy,eliasdorneles/scrapy,fpy171/scrapy,cyberplant/scrapy,tagatac/scrapy,darkrho/scrapy-scrapy,bmess/scrapy,pfctdayelise/scrapy,OpenWhere/scrapy,kmike/scrapy,ENjOyAbLE1991/scrapy,godfreyy/scrapy,nguyenhongson03/scrapy,tagatac/scrapy,joshlk/scrapy,KublaikhanGeek/scrapy,wangjun/scrapy,kmike/scrapy,AaronTao1990/scrapy,ENjOyAbLE1991/scrapy,KublaikhanGeek/scrapy,Allianzcortex/scrapy,CodeJuan/scrapy,coderabhishek/scrapy,chekunkov/scrapy,wzyuliyang/scrapy,Preetwinder/scrapy,taito/scrapy,cursesun/scrapy,Partoo/scrapy,github-account-because-they-want-it/scrapy,mouadino/scrapy,jamesblunt/scrapy,ndemir/scrapy,songfj/scrapy,eLRuLL/scrapy,olafdietsche/scrapy,dacjames/scrapy,redapple/scrapy,scrapy/scrapy,kazitanvirahsan/scrapy,Digenis/scrapy,wenyu1001/scrapy,ndemir/scrapy,umrashrf/scrapy,GregoryVigoTorres/scrapy,wujuguang/scrapy,foromer4/scrapy,zackslash/scrapy,hwsyy/scrapy,fafaman/scrapy,olafdietsche/scrapy,wzyuliyang/scrapy,moraesnicol/scrapy,songfj/scrapy,emschorsch/scrapy,sardok/scrapy,nowopen/scrapy,rolando/scrapy,csalazar/scrapy,nfunato/scrapy,zorojean/scrapy,Parlin-Galanodel/scrapy,wenyu1001/scrapy,avtoritet/scrapy,snowdream1314/scrapy,agreen/scrapy,nowopen/scrapy,JacobStevenR/scrapy,heamon7/scrapy,scorphus/scrapy,Geeglee/scrapy,stenskjaer/scrapy,chekunkov/scrapy,pranjalpatil/scrapy,kimimj/scrapy,dracony/scrapy,huoxudong125/scrapy,shaform/scrapy,livepy/scrapy,agreen/scrapy,johnardavies/scrapy,arush0311/scrapy,jeffreyjinfeng/scrapy,finfish/scrapy,devGregA/scrapy,curita/scrapy,1yvT0s/scrapy,Allianzcortex/scrapy,hyrole/scrapy,rdowinton/scrapy,jc0n/scrapy,1yvT0s/scrapy,nikgr95/scrapy,kmike/scrapy,godfreyy/scrapy,WilliamKinaan/scrapy,jiezhu2007/scrapy,crasker/scrapy,dracony/scrapy,hectoruelo/scrapy,bmess/scrapy,aivarsk/scrapy,ylcolala/scrapy,webmakin/scrapy,moraesnicol/scrapy,wenyu1001/scrapy,w495/scrapy,rootAvish/scrapy,avtoritet/scrapy,profjrr/scrapy,darkrho/scrapy-scrapy,github-account-because-they-want-it/scrapy,webmakin/scrapy,pablohoffman/scrapy,rolando-contrib/scrapy,Zephor5/scrapy,wangjun/scrapy,URXtech/scrapy,heamon7/scrapy,yarikoptic/scrapy,scrapy/scrapy,Adai0808/scrapy-1,URXtech/scrapy,wujuguang/scrapy,agusc/scrapy,nikgr95/scrapy,kimimj/scrapy,AaronTao1990/scrapy,foromer4/scrapy,zhangtao11/scrapy,foromer4/scrapy,Slater-Victoroff/scrapy,scorphus/scrapy,gbirke/scrapy,cyrixhero/scrapy,xiao26/scrapy,dangra/scrapy,mlyundin/scrapy,AaronTao1990/scrapy,hectoruelo/scrapy,dacjames/scrapy,Geeglee/scrapy,fontenele/scrapy,scrapy/scrapy,carlosp420/scrapy,ramiro/scrapy,yusofm/scrapy,crasker/scrapy,gbirke/scrapy,Djlavoy/scrapy,yarikoptic/scrapy,kalessin/scrapy,ramiro/scrapy,OpenWhere/scrapy,emschorsch/scrapy,rahul-c1/scrapy,Bourneer/scrapy,smaty1/scrapy,famorted/scrapy,joshlk/scrapy,irwinlove/scrapy,livepy/scrapy,Ryezhang/scrapy,nett55/scrapy,1yvT0s/scrapy,Chenmxs/scrapy,nguyenhongson03/scrapy,kashyap32/scrapy,rdowinton/scrapy,starrify/scrapy,tntC4stl3/scrapy,Adai0808/scrapy-1,finfish/scrapy,mgedmin/scrapy,OpenWhere/scrapy,nowopen/scrapy,barraponto/scrapy,jorik041/scrapy,mlyundin/scrapy,Preetwinder/scrapy,z-fork/scrapy,irwinlove/scrapy,ylcolala/scrapy,pfctdayelise/scrapy,sigma-random/scrapy,hectoruelo/scrapy,snowdream1314/scrapy,csalazar/scrapy,crasker/scrapy,JacobStevenR/scrapy,chekunkov/scrapy,Geeglee/scrapy,zjuwangg/scrapy,Ryezhang/scrapy,yidongliu/scrapy,lacrazyboy/scrapy,kashyap32/scrapy,profjrr/scrapy,ashishnerkar1/scrapy,legendtkl/scrapy,IvanGavran/scrapy,Parlin-Galanodel/scrapy,coderabhishek/scrapy,ssh-odoo/scrapy,hbwzhsh/scrapy,URXtech/scrapy,rklabs/scrapy,redapple/scrapy,Djlavoy/scrapy,shaform/scrapy,pombredanne/scrapy,starrify/scrapy,snowdream1314/scrapy,irwinlove/scrapy,Cnfc19932/scrapy,pombredanne/scrapy,KublaikhanGeek/scrapy,godfreyy/scrapy,eliasdorneles/scrapy,dhenyjarasandy/scrapy,fafaman/scrapy,IvanGavran/scrapy,yidongliu/scrapy,ssh-odoo/scrapy,livepy/scrapy,haiiiiiyun/scrapy,Zephor5/scrapy,beni55/scrapy,tagatac/scrapy,fqul/scrapy,legendtkl/scrapy,GregoryVigoTorres/scrapy,jeffreyjinfeng/scrapy,aivarsk/scrapy,CENDARI/scrapy,pawelmhm/scrapy,jeffreyjinfeng/scrapy,barraponto/scrapy,YeelerG/scrapy,elijah513/scrapy,jc0n/scrapy,Preetwinder/scrapy,gnemoug/scrapy,ssh-odoo/scrapy,wzyuliyang/scrapy,jdemaeyer/scrapy,fpy171/scrapy,kazitanvirahsan/scrapy,zhangtao11/scrapy,stenskjaer/scrapy,taito/scrapy,avtoritet/scrapy,fafaman/scrapy,farhan0581/scrapy,joshlk/scrapy,eLRuLL/scrapy,WilliamKinaan/scrapy,agreen/scrapy,nett55/scrapy,Timeship/scrapy,Adai0808/scrapy-1,hwsyy/scrapy,rahulsharma1991/scrapy,kazitanvirahsan/scrapy,smaty1/scrapy,cyrixhero/scrapy,Zephor5/scrapy,huoxudong125/scrapy,dgillis/scrapy,Lucifer-Kim/scrapy,tliber/scrapy,shaform/scrapy,yidongliu/scrapy,liyy7/scrapy,ashishnerkar1/scrapy,olorz/scrapy,ramiro/scrapy,wujuguang/scrapy,xiao26/scrapy,TarasRudnyk/scrapy,fqul/scrapy,fqul/scrapy,nikgr95/scrapy,Partoo/scrapy,ssteo/scrapy,Cnfc19932/scrapy,ssteo/scrapy,raphaelfruneaux/scrapy,emschorsch/scrapy,zhangtao11/scrapy,yarikoptic/scrapy,lacrazyboy/scrapy,Digenis/scrapy,Timeship/scrapy,codebhendi/scrapy,zjuwangg/scrapy,ArturGaspar/scrapy,redapple/scrapy,curita/scrapy,rootAvish/scrapy,mlyundin/scrapy,tntC4stl3/scrapy,devGregA/scrapy,taito/scrapy,Slater-Victoroff/scrapy,elacuesta/scrapy,ylcolala/scrapy,zorojean/scrapy,kalessin/scrapy,xiao26/scrapy,jdemaeyer/scrapy,liyy7/scrapy,hwsyy/scrapy,JacobStevenR/scrapy,codebhendi/scrapy,YeelerG/scrapy,devGregA/scrapy,CENDARI/scrapy,coderabhishek/scrapy,hansenDise/scrapy,agusc/scrapy,yusofm/scrapy,agusc/scrapy,dracony/scrapy,legendtkl/scrapy,z-fork/scrapy,fontenele/scrapy,ssteo/scrapy,csalazar/scrapy,rklabs/scrapy,smaty1/scrapy,CENDARI/scrapy,raphaelfruneaux/scrapy,Timeship/scrapy,kimimj/scrapy,johnardavies/scrapy,aivarsk/scrapy,cyberplant/scrapy,rahulsharma1991/scrapy,bmess/scrapy,zackslash/scrapy,haiiiiiyun/scrapy,haiiiiiyun/scrapy,Parlin-Galanodel/scrapy,dhenyjarasandy/scrapy,amboxer21/scrapy,ArturGaspar/scrapy,lacrazyboy/scrapy,rolando/scrapy,cursesun/scrapy,kalessin/scrapy,pranjalpatil/scrapy,yusofm/scrapy,w495/scrapy,CodeJuan/scrapy,Cnfc19932/scrapy,nett55/scrapy,starrify/scrapy,olorz/scrapy,pablohoffman/scrapy,Allianzcortex/scrapy,cleydson/scrapy,tliber/scrapy,mgedmin/scrapy,jiezhu2007/scrapy,jiezhu2007/scrapy,eliasdorneles/scrapy,curita/scrapy,scorphus/scrapy,beni55/scrapy,raphaelfruneaux/scrapy,profjrr/scrapy,rklabs/scrapy,elijah513/scrapy,Lucifer-Kim/scrapy,moraesnicol/scrapy,rahulsharma1991/scrapy,rootAvish/scrapy,zackslash/scrapy,famorted/scrapy,pawelmhm/scrapy,rahul-c1/scrapy,fontenele/scrapy,hbwzhsh/scrapy,jamesblunt/scrapy,hansenDise/scrapy,carlosp420/scrapy,TarasRudnyk/scrapy,nguyenhongson03/scrapy,github-account-because-they-want-it/scrapy,dacjames/scrapy,songfj/scrapy,dangra/scrapy,pombredanne/scrapy,finfish/scrapy,pablohoffman/scrapy,mgedmin/scrapy,beni55/scrapy,mouadino/scrapy,CodeJuan/scrapy,rolando-contrib/scrapy,sardok/scrapy,umrashrf/scrapy,stenskjaer/scrapy,YeelerG/scrapy,rahul-c1/scrapy,Lucifer-Kim/scrapy,fpy171/scrapy,olorz/scrapy,gnemoug/scrapy,sigma-random/scrapy,amboxer21/scrapy,barraponto/scrapy,cyberplant/scrapy,jorik041/scrapy,cleydson/scrapy,Bourneer/scrapy,Digenis/scrapy,jc0n/scrapy,farhan0581/scrapy,w495/scrapy,farhan0581/scrapy,jdemaeyer/scrapy,Slater-Victoroff/scrapy,tntC4stl3/scrapy,eLRuLL/scrapy,rolando/scrapy,dgillis/scrapy,Partoo/scrapy,dgillis/scrapy,arush0311/scrapy,Bourneer/scrapy,johnardavies/scrapy,cleydson/scrapy,Djlavoy/scrapy,z-fork/scrapy,tliber/scrapy,ENjOyAbLE1991/scrapy,liyy7/scrapy,arush0311/scrapy,dhenyjarasandy/scrapy,famorted/scrapy,codebhendi/scrapy,Chenmxs/scrapy,GregoryVigoTorres/scrapy,olafdietsche/scrapy,nfunato/scrapy,Chenmxs/scrapy,cyrixhero/scrapy,pawelmhm/scrapy,hyrole/scrapy,amboxer21/scrapy,zorojean/scrapy,hansenDise/scrapy,jorik041/scrapy,TarasRudnyk/scrapy,darkrho/scrapy-scrapy,ArturGaspar/scrapy,zjuwangg/scrapy,IvanGavran/scrapy,wangjun/scrapy,cursesun/scrapy,webmakin/scrapy,elacuesta/scrapy,huoxudong125/scrapy,elacuesta/scrapy,umrashrf/scrapy,pranjalpatil/scrapy