[PATCH] First step towards adding a parent map to the ASTContext.

[Edwin Vane]

  I don't know anything about the analyzer but it sounds like it is what is driving the design. For tools this all looks good if only a little heavy-handed. Your suggestions for improvements that would make parent map construction not touch the whole AST would be welcome.

  Question: does MatchASTVisitor::matchesAncestorOf() need fixing to use the new ASTContext::getParents()?

http://llvm-reviews.chandlerc.com/D267