Implement typo correction for Objective-C message sends when the

receiver is a mis-typed class name. Previously, we would give a non-specific
typo-correction diagnostic from the expression-parsing code, but there
was no fix-it because it was too late to recover. Now, we give a nice
diagnostic

honk.m:6:4: error: unknown receiver 'Hnk'; did you mean 'Honk'?
  [Hnk method];
   ^~~
   Honk
honk.m:1:1: note: 'Honk' declared here
@interface Honk
^

which includes a fix-it.

We still need to recover better from mis-typing "super".

llvm-svn: 101211