A quick fix to allow return type deduction on member templates

by ensuring DiagnoseUseOfDecl is called both on the found decl and the
decl being used (i.e the specialization in the case of member templates) whenever they are different.
Per the exchange captured in
http://lists.cs.uiuc.edu/pipermail/cfe-commits/Week-of-Mon-20130610/081636.html
a more comprehensive fix that allows both decls to be passed into DiagnoseUseOfDecl is (or should be) forthcoming relatively soon.

llvm-svn: 184043