Refine analyzer diagnostics by adding an expression "cone-of-influence" to...

Refine analyzer diagnostics by adding an expression "cone-of-influence" to reverse track interesting
values through interesting expressions.  This allows us to map from interesting values in a caller
to interesting values in a caller, thus recovering some precision in diagnostics lost from IPA.

Fixes <rdar://problem/11327497>

llvm-svn: 155971