Better error message for invalid “return” trait mod
Better error message for invalid “return” trait mod

Previously it either complained about a missing block or spewed some
internal gibberish. Now it suggests “returns”.

Resolves RT #130712

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