swift234

This is a WIP implementation of a major change to how ObjC properties are
represented: they should have an explicit getter and setter synthesized by
Sema, instead of by silgen and tenuously tied in by IRGen.

There is more work to be done on this (e.g. I need to figure out how to get
the bodies properly type checked), so it is hidden behind a new
-enable-new-objc-properties flag.



Swift SVN r12907