swift234

Teach name lookup to remove overridden methods in extensions from its results.

While we haven't worked out the details of whether methods in
extensions can be overridden in Swift, it's something that does happen
in Objective-C, so we need to deal with it.

With this change, note that our demo application can both allocate
Objective-C objects with "new" (which John recently fixed) and also
subscript mutable arrays to both read and write.


Swift SVN r3485