Streamline CU::RepositoryRegistry.use-repository a bit
Streamline CU::RepositoryRegistry.use-repository a bit

- don't use return when we don't need to
- don't use named parameters or default when we don't need to
- add some extra type checking
- use binding where possible

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