swift234

Runtime: Handle casting from class types to class metatypes.

Implement casting support for taking an AnyObject and conditionally converting it to a T.Type for some class type. Fix some memory management bugs too, where we used swift_release to release an object not known to have Swift refcounting. This mostly fixes rdar://problem/16238475, though the SIL optimizer still improperly folds away attempted casts from NSObject to a class metatype, and I haven't yet validated bridging support for NSArray<Class>*.

Swift SVN r29956