Fix closure handling of the s/// construct
Fix closure handling of the s/// construct

This fixes #3475. It may well also fix more than that, since it turned
out to be a more general problem with scoping of blocks in thunks.

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