swift234

[PrintAsObjC] Only print inner classes if they are explicitly marked @objc.

This reduces the chances of conflict among inner class names. It's too easy
for a class to be implicitly marked @objc in Swift.

To make this work, correctly preserve the implicitness of @objc through
serialization. (We were probably intending to do this all along, since we
were serializing the flag but not doing anything with it at the other end.)

Swift SVN r21678