Slight tweak to ASSIGN-KEY
Slight tweak to ASSIGN-KEY

Generates simpler code, so is faster unspecialized, and specializes a
bit better too.

tbrowder/rakudo,softmoth/rakudo,tony-o/rakudo,salortiz/rakudo,Gnouc/rakudo,nbrown/rakudo,softmoth/rakudo,rakudo/rakudo,nbrown/rakudo,rakudo/rakudo,tony-o/rakudo,salortiz/rakudo,labster/rakudo,rakudo/rakudo,salortiz/rakudo,MasterDuke17/rakudo,Gnouc/rakudo,rakudo/rakudo,tbrowder/rakudo,MasterDuke17/rakudo,rakudo/rakudo,tony-o/rakudo,MasterDuke17/rakudo,tbrowder/rakudo,tbrowder/rakudo,nbrown/rakudo,MasterDuke17/rakudo,salortiz/rakudo,tbrowder/rakudo,Gnouc/rakudo,labster/rakudo,salortiz/rakudo,Gnouc/rakudo,labster/rakudo,tony-o/rakudo,softmoth/rakudo,tony-o/rakudo,labster/rakudo,rakudo/rakudo,nbrown/rakudo,labster/rakudo,Gnouc/rakudo,softmoth/rakudo,salortiz/rakudo,softmoth/rakudo,nbrown/rakudo,Gnouc/rakudo,tony-o/rakudo,MasterDuke17/rakudo,labster/rakudo,nbrown/rakudo,tbrowder/rakudo,MasterDuke17/rakudo