swift234

[serialization] Accept @weak and @unowned on VarDecls.

We don't actually need to serialize these because they've already been
encoded in the VarDecl's type. However, we'll probably need to be careful
when pretty-printing these on the other side.

Also, be more precise about checking @class_protocol serialization --
before we'd accept any failure, not just rejecting the struct conformance.

Swift SVN r9356