swift234

Always Objective-C categories for extensions with [objc] entry points.

Previously, we predicated this on the original class itself being
[objc] or the extension having adopted any [objc] protocols. Extend
that definition to consider one-off, explicitly-marked [objc] methods
or properties.

Since we're here, and make sure we can reference the Objective-C
metaclass in the interpreter even when the original class wasn't
marked [objc].



Swift SVN r8310