Adds the equalsBoundNode matcher.

Most of the tests contributed by Edwin Vane.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@184427 91177308-0d34-0410-b5e6-96231b3b80d8
Enhancements for the DynTypedMatcher system.
- Added conversion routines and checks in Matcher<T> that take a DynTypedMatcher.
- Added type information on the error messages for the marshallers.
- Allows future work on Polymorphic/overloaded matchers. We should be
  able to disambiguate at runtime and choose the appropriate overload.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@184429 91177308-0d34-0410-b5e6-96231b3b80d8