Make DynTypedNode have the dynamic type of the object, instead of its static type.

Summary:
Make DynTypedNode have the dynamic type of the object, instead of its static type.
Some optimizations that are in the works require that the nodes have the right type.

Reviewers: klimek

Subscribers: cfe-commits

Differential Revision: http://reviews.llvm.org/D5411

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@218127 91177308-0d34-0410-b5e6-96231b3b80d8