Revert "Remove .pop's "is rw" and fix the fallout from unshift's use of that"
Revert "Remove .pop's "is rw" and fix the fallout from unshift's use of that"

This reverts commit 68301a78dc644229fa747250d7119500103f2baa.

paultcochrane/rakudo,salortiz/rakudo,tony-o/rakudo,ungrim97/rakudo,paultcochrane/rakudo,raydiak/rakudo,Gnouc/rakudo,tony-o/rakudo,Leont/rakudo,zhuomingliang/rakudo,azawawi/rakudo,jonathanstowe/rakudo,jonathanstowe/rakudo,skids/rakudo,ab5tract/rakudo,ugexe/rakudo,zostay/rakudo,nbrown/rakudo,sergot/rakudo,rakudo/rakudo,zhuomingliang/rakudo,teodozjan/rakudo,laben/rakudo,skids/rakudo,skids/rakudo,zostay/rakudo,MasterDuke17/rakudo,raydiak/rakudo,b2gills/rakudo,zostay/rakudo,retupmoca/rakudo,usev6/rakudo,usev6/rakudo,ungrim97/rakudo,LLFourn/rakudo,zostay/rakudo,salortiz/rakudo,nbrown/rakudo,laben/rakudo,samcv/rakudo,ugexe/rakudo,dankogai/rakudo,samcv/rakudo,b2gills/rakudo,rakudo/rakudo,tbrowder/rakudo,cognominal/rakudo,tbrowder/rakudo,tbrowder/rakudo,cygx/rakudo,azawawi/rakudo,lucasbuchala/rakudo,Leont/rakudo,niner/rakudo,awwaiid/rakudo,dankogai/rakudo,rakudo/rakudo,paultcochrane/rakudo,ab5tract/rakudo,tony-o/deb-rakudodaily,dwarring/rakudo,ungrim97/rakudo,laben/rakudo,sergot/rakudo,sergot/rakudo,samcv/rakudo,dankogai/rakudo,retupmoca/rakudo,softmoth/rakudo,labster/rakudo,ungrim97/rakudo,usev6/rakudo,tbrowder/rakudo,skids/rakudo,cygx/rakudo,tony-o/deb-rakudodaily,LLFourn/rakudo,tony-o/deb-rakudodaily,tony-o/rakudo,Gnouc/rakudo,samcv/rakudo,nunorc/rakudo,LLFourn/rakudo,retupmoca/rakudo,rakudo/rakudo,niner/rakudo,Gnouc/rakudo,nunorc/rakudo,Gnouc/rakudo,nbrown/rakudo,usev6/rakudo,softmoth/rakudo,b2gills/rakudo,ugexe/rakudo,sjn/rakudo,pmurias/rakudo,rakudo/rakudo,cygx/rakudo,cygx/rakudo,pmurias/rakudo,niner/rakudo,ugexe/rakudo,sjn/rakudo,salortiz/rakudo,labster/rakudo,labster/rakudo,sjn/rakudo,awwaiid/rakudo,samcv/rakudo,ab5tract/rakudo,labster/rakudo,ab5tract/rakudo,Leont/rakudo,tony-o/deb-rakudodaily,cognominal/rakudo,MasterDuke17/rakudo,nbrown/rakudo,cognominal/rakudo,cygx/rakudo,paultcochrane/rakudo,rakudo/rakudo,cognominal/rakudo,MasterDuke17/rakudo,labster/rakudo,paultcochrane/rakudo,niner/rakudo,sjn/rakudo,lucasbuchala/rakudo,laben/rakudo,Gnouc/rakudo,softmoth/rakudo,zhuomingliang/rakudo,b2gills/rakudo,raydiak/rakudo,tony-o/rakudo,retupmoca/rakudo,nunorc/rakudo,ungrim97/rakudo,nbrown/rakudo,MasterDuke17/rakudo,tony-o/rakudo,teodozjan/rakudo,azawawi/rakudo,tony-o/rakudo,nunorc/rakudo,zhuomingliang/rakudo,LLFourn/rakudo,azawawi/rakudo,tony-o/deb-rakudodaily,pmurias/rakudo,teodozjan/rakudo,softmoth/rakudo,salortiz/rakudo,lucasbuchala/rakudo,usev6/rakudo,salortiz/rakudo,azawawi/rakudo,jonathanstowe/rakudo,skids/rakudo,dwarring/rakudo,labster/rakudo,cognominal/rakudo,pmurias/rakudo,ugexe/rakudo,awwaiid/rakudo,Gnouc/rakudo,jonathanstowe/rakudo,dankogai/rakudo,nbrown/rakudo,salortiz/rakudo,tbrowder/rakudo,lucasbuchala/rakudo,lucasbuchala/rakudo,awwaiid/rakudo,MasterDuke17/rakudo,tony-o/deb-rakudodaily,dankogai/rakudo,softmoth/rakudo,dwarring/rakudo,awwaiid/rakudo,Leont/rakudo,teodozjan/rakudo,ab5tract/rakudo,raydiak/rakudo,sergot/rakudo,tbrowder/rakudo,LLFourn/rakudo,MasterDuke17/rakudo,b2gills/rakudo,jonathanstowe/rakudo,sjn/rakudo,dwarring/rakudo,tony-o/deb-rakudodaily