retain/release checker:

- Fix summary lookup for class methods to now use the (optional)
  ObjCInterfaceDecl associated with a message expression. This removes a
  long-standing FIXME.
- Partial fix for <rdar://problem/6062730> by stop tracking objects that
  are passed to [NSObject performSelector].  These methods are often used
  for delegates, which the analyzer doesn't reason about well yet.

llvm-svn: 69982