Fix binding of nodes in case of forEach..() matchers.

When recursively visiting the generated matches, the aggregated bindings need
to be copied during the recursion. Otherwise, we they might not be properly
overwritten (which is shown by the test), or there might be bound nodes present
that were bound on a different matching branch.

Review: http://llvm-reviews.chandlerc.com/D112
llvm-svn: 167695