Fix Sema::ActOnClassMessage() to pass through the identifier for "super".

This fixes a critical rewriter bug (<rdar://problem/6096760> clang ObjC rewriter: 'self' not expected value in class method called with 'super').

Also added a couple FIXME's since I'm not happy with my fix to Sema. It would be nicer if the super handling for class/instance messages was the same (based on PreDefinedExpr).

llvm-svn: 53994