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

llvm-svn: 218127