Provide a naming class for UnresolvedLookupExprs, even when occuring on

template names. We were completely missing naming classes for many unqualified
lookups, but this didn't trigger code paths that need it. This removes part of
an optimization that re-uses the template name lookup done by the parser to
determine if explicit template arguments actually form a template-id.
Unfortunately the technique for avoiding the duplicate lookup lost needed data
such as the class context in which the lookup succeeded.

llvm-svn: 104117