Make List.FLATTENABLE_LIST a bit cheaper
Make List.FLATTENABLE_LIST a bit cheaper

If there's a $!todo, there will be a $!reified created anyway, so
no need to check for $!reified.DEFINITE then.  Also part of the effort
to get rid of !ensure-allocated.

tony-o/rakudo,lucasbuchala/rakudo,jonathanstowe/rakudo,samcv/rakudo,usev6/rakudo,sjn/rakudo,awwaiid/rakudo,raydiak/rakudo,usev6/rakudo,softmoth/rakudo,MasterDuke17/rakudo,awwaiid/rakudo,tbrowder/rakudo,usev6/rakudo,zostay/rakudo,sjn/rakudo,tbrowder/rakudo,MasterDuke17/rakudo,jonathanstowe/rakudo,lucasbuchala/rakudo,rakudo/rakudo,labster/rakudo,jonathanstowe/rakudo,raydiak/rakudo,MasterDuke17/rakudo,rakudo/rakudo,b2gills/rakudo,rakudo/rakudo,samcv/rakudo,awwaiid/rakudo,tony-o/rakudo,sjn/rakudo,b2gills/rakudo,tbrowder/rakudo,salortiz/rakudo,tony-o/rakudo,labster/rakudo,salortiz/rakudo,MasterDuke17/rakudo,zostay/rakudo,tony-o/rakudo,tbrowder/rakudo,Gnouc/rakudo,salortiz/rakudo,labster/rakudo,salortiz/rakudo,raydiak/rakudo,samcv/rakudo,softmoth/rakudo,zostay/rakudo,Gnouc/rakudo,lucasbuchala/rakudo,lucasbuchala/rakudo,samcv/rakudo,salortiz/rakudo,softmoth/rakudo,awwaiid/rakudo,salortiz/rakudo,Gnouc/rakudo,jonathanstowe/rakudo,sjn/rakudo,b2gills/rakudo,tbrowder/rakudo,b2gills/rakudo,nbrown/rakudo,jonathanstowe/rakudo,nbrown/rakudo,rakudo/rakudo,Gnouc/rakudo,labster/rakudo,Gnouc/rakudo,nbrown/rakudo,sjn/rakudo,awwaiid/rakudo,rakudo/rakudo,MasterDuke17/rakudo,nbrown/rakudo,MasterDuke17/rakudo,samcv/rakudo,raydiak/rakudo,tony-o/rakudo,softmoth/rakudo,b2gills/rakudo,Gnouc/rakudo,rakudo/rakudo,usev6/rakudo,softmoth/rakudo,tbrowder/rakudo,tony-o/rakudo,zostay/rakudo,nbrown/rakudo,lucasbuchala/rakudo,labster/rakudo,usev6/rakudo,labster/rakudo,nbrown/rakudo