Fix a case where delayed typo correction should have resolved an

ambiguity but wasn't.

In the new test case, "click" wasn't being corrected properly because
Sema::ClassifyName would call CorrectTypo for "click" then later
Sema::DiagnoseEmptyLookup would call CorrectTypoDelayed for the same use
of "click" (the former by the parser needing to determine what the
identifier is so it knows how to parse the statement, i.e. is it the
beginning of a declaration or an expression). CorrectTypo would record
that typo correction for "click" failed and CorrectTypoDelayed would see
that and not even try to correct the typo, even though in this case
CorrectTypo failed due to an ambiguity (both "Click" and "clock" having
an edit distance of one from "click") that could be resolved with more
information. The fix is two-fold:
  1) Have CorrectTypo not record failed corrections if the reason for
     the failure was two or more corrections with the same edit
     distance, and
  2) Make the CorrectionCandidateCallback used by
     Parser::ParseCastExpression reject FunctionDecl candidates when the
     next token after the identifier is a ".", "=", or "->" since
     functions cannot be assigned to and do not have members that can be
     referenced.

The reason for two correction spots is that from r222549 until r224375
landed, the first correction attempt would fail completely but the
second would suggest "clock" while having the note point to the
declaration of "Click".

llvm-svn: 226334