Implement typo correction for a variety of Objective-C-specific

constructs:

  - Instance variable lookup ("foo->ivar" and, in instance methods, "ivar")
  - Property name lookup ("foo.prop")
  - Superclasses
  - Various places where a class name is required
  - Protocol names (e.g., id<proto>)

This seems to cover many of the common places where typos could occur.

llvm-svn: 92449