Run MainScheduler actions immediately if allowed
Run MainScheduler actions immediately if allowed

Resolves #1619.

CCOOOOLL/ReactiveCocoa,libiao88/ReactiveCocoa,juliangrosshauser/ReactiveCocoa,kaylio/ReactiveCocoa,KuPai32G/ReactiveCocoa,hilllinux/ReactiveCocoa,stevielu/ReactiveCocoa,j364960953/ReactiveCocoa,ceekayel/ReactiveCocoa,ikesyo/ReactiveCocoa,ohwutup/ReactiveCocoa,xiaoliyang/ReactiveCocoa,JackLian/ReactiveCocoa,fanghao085/ReactiveCocoa,mtxs007/ReactiveCocoa,cogddo/ReactiveCocoa,leelili/ReactiveCocoa,msdgwzhy6/ReactiveCocoa,icepy/ReactiveCocoa,leichunfeng/ReactiveCocoa,almassapargali/ReactiveCocoa,valleyman86/ReactiveCocoa,smilypeda/ReactiveCocoa,nikita-leonov/ReactiveCocoa,monkeydbobo/ReactiveCocoa,DongDongDongDong/ReactiveCocoa,leichunfeng/ReactiveCocoa,Liquidsoul/ReactiveCocoa,sandyway/ReactiveCocoa,Eveian/ReactiveCocoa,hbucius/ReactiveCocoa,nikita-leonov/ReactiveCocoa,cogddo/ReactiveCocoa,goodheart/ReactiveCocoa,ztchena/ReactiveCocoa,CQXfly/ReactiveCocoa,qq644531343/ReactiveCocoa,zhenlove/ReactiveCocoa,SanChain/ReactiveCocoa,cnbin/ReactiveCocoa,juliangrosshauser/ReactiveCocoa,BrooksWon/ReactiveCocoa,Liquidsoul/ReactiveCocoa,nickcheng/ReactiveCocoa,victorlin/ReactiveCocoa,juliangrosshauser/ReactiveCocoa,yangshengchaoios/ReactiveCocoa,Farteen/ReactiveCocoa,longv2go/ReactiveCocoa,natan/ReactiveCocoa,add715/ReactiveCocoa,takeshineshiro/ReactiveCocoa,calebd/ReactiveCocoa,buildo/ReactiveCocoa,200895045/ReactiveCocoa,bscarano/ReactiveCocoa,pzw224/ReactiveCocoa,hj3938/ReactiveCocoa,andersio/ReactiveCocoa,tonyli508/ReactiveCocoa,luerhouhou/ReactiveCocoa,200895045/ReactiveCocoa,huiping192/ReactiveCocoa,calebd/ReactiveCocoa,natestedman/ReactiveCocoa,towik/ReactiveCocoa,zhiwen1024/ReactiveCocoa,jam891/ReactiveCocoa,ddc391565320/ReactiveCocoa,j364960953/ReactiveCocoa,ReactiveCocoa/ReactiveSwift,imkerberos/ReactiveCocoa,dachaoisme/ReactiveCocoa,alvinvarghese/ReactiveCocoa,sdhzwm/ReactiveCocoa,OneSmallTree/ReactiveCocoa,dz1111/ReactiveCocoa,tonyarnold/ReactiveCocoa,stupidfive/ReactiveCocoa,llb1119/test,yizzuide/ReactiveCocoa,WEIBP/ReactiveCocoa,DongDongDongDong/ReactiveCocoa,yangyangluoluo/ReactiveCocoa,rpowelll/ReactiveCocoa,emodeqidao/ReactiveCocoa,GuitarPlayer-Ma/ReactiveCocoa,kevin-zqw/ReactiveCocoa,dullgrass/ReactiveCocoa,AndyZhaoHe/ReactiveCocoa,andersio/ReactiveCocoa,terry408911/ReactiveCocoa,tzongw/ReactiveCocoa,nickcheng/ReactiveCocoa,kiurentu/ReactiveCocoa,loupman/ReactiveCocoa,zzzworm/ReactiveCocoa,sdhzwm/ReactiveCocoa,imkerberos/ReactiveCocoa,KuPai32G/ReactiveCocoa,emodeqidao/ReactiveCocoa,alvinvarghese/ReactiveCocoa,jsslai/ReactiveCocoa,wpstarnice/ReactiveCocoa,chieryw/ReactiveCocoa,dz1111/ReactiveCocoa,RuiAAPeres/ReactiveCocoa,loupman/ReactiveCocoa,tonyarnold/ReactiveCocoa,yaoxiaoyong/ReactiveCocoa,llb1119/test,beni55/ReactiveCocoa,gengjf/ReactiveCocoa,huiping192/ReactiveCocoa,gengjf/ReactiveCocoa,chao95957/ReactiveCocoa,Khan/ReactiveCocoa,wpstarnice/ReactiveCocoa,DreamHill/ReactiveCocoa,yangyangluoluo/ReactiveCocoa,Ricowere/ReactiveCocoa,Khan/ReactiveCocoa,liufeigit/ReactiveCocoa,ceekayel/ReactiveCocoa,ShawnLeee/ReactiveCocoa,DreamHill/ReactiveCocoa,on99/ReactiveCocoa,smilypeda/ReactiveCocoa,CCOOOOLL/ReactiveCocoa,howandhao/ReactiveCocoa,andersio/ReactiveCocoa,Ray0218/ReactiveCocoa,wangqi211/ReactiveCocoa,dullgrass/ReactiveCocoa,smilypeda/ReactiveCocoa,kevin-zqw/ReactiveCocoa,bensonday/ReactiveCocoa,nickcheng/ReactiveCocoa,cnbin/ReactiveCocoa,ztchena/ReactiveCocoa,brasbug/ReactiveCocoa,jaylib/ReactiveCocoa,zzqiltw/ReactiveCocoa,fanghao085/ReactiveCocoa,bscarano/ReactiveCocoa,yaoxiaoyong/ReactiveCocoa,JohnJin007/ReactiveCocoa,jeelun/ReactiveCocoa,howandhao/ReactiveCocoa,hbucius/ReactiveCocoa,hoanganh6491/ReactiveCocoa,paulyoung/ReactiveCocoa,zhaoguohui/ReactiveCocoa,sandyway/ReactiveCocoa,vincentiss/ReactiveCocoa,zhigang1992/ReactiveCocoa,dullgrass/ReactiveCocoa,pzw224/ReactiveCocoa,mxxiv/ReactiveCocoa,Juraldinio/ReactiveCocoa,paulyoung/ReactiveCocoa,mattpetters/ReactiveCocoa,Ricowere/ReactiveCocoa,vincentiss/ReactiveCocoa,luerhouhou/ReactiveCocoa,Pingco/ReactiveCocoa,SanChain/ReactiveCocoa,KJin99/ReactiveCocoa,jam891/ReactiveCocoa,llb1119/test,tonyli508/ReactiveCocoa,clg0118/ReactiveCocoa,OnTheWay1988/ReactiveCocoa,PSPDFKit-labs/ReactiveCocoa,walkingsmarts/ReactiveCocoa,bscarano/ReactiveCocoa,ShawnLeee/ReactiveCocoa,zhiwen1024/ReactiveCocoa,Ray0218/ReactiveCocoa,loupman/ReactiveCocoa,monkeydbobo/ReactiveCocoa,wangqi211/ReactiveCocoa,yonekawa/ReactiveCocoa,jaylib/ReactiveCocoa,stupidfive/ReactiveCocoa,SuPair/ReactiveCocoa,longv2go/ReactiveCocoa,xulibao/ReactiveCocoa,mxxiv/ReactiveCocoa,BlessNeo/ReactiveCocoa,jsslai/ReactiveCocoa,yoichitgy/ReactiveCocoa,add715/ReactiveCocoa,fhchina/ReactiveCocoa,chieryw/ReactiveCocoa,cstars135/ReactiveCocoa,kaylio/ReactiveCocoa,xiaobing2007/ReactiveCocoa,AlanJN/ReactiveCocoa,cnbin/ReactiveCocoa,goodheart/ReactiveCocoa,FelixYin66/ReactiveCocoa,cstars135/ReactiveCocoa,Ethan89/ReactiveCocoa,ceekayel/ReactiveCocoa,xulibao/ReactiveCocoa,add715/ReactiveCocoa,ReactiveCocoa/ReactiveSwift,huiping192/ReactiveCocoa,isghe/ReactiveCocoa,natestedman/ReactiveCocoa,fhchina/ReactiveCocoa,LHDsim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