swift234

[ClangImporter] Import class, protocol, and category members lazily.

This still isn't /that/ lazy because a lot of things can force member
deserialization (such as the type-checker generating a DestructorDecl for
every imported class), and we don't do this in a member-granular way just
yet. I don't see any change in testing time, for example.

But besides just being a good thing in general, this perturbs the order
of imported decls enough to fix <rdar://problem/15799697>: we can now
reliably see that there is a -URL:something: function on NSObject that
blocks any properties named 'URL' from being imported as properties.

(Which we don't actually want; see <rdar://problem/15456130>.)

Swift SVN r12685