During template instantiation, set the naming class of

UnresolvedLookupExpr and UnresolvedMemberExpr by substituting the
naming class we computed when building the expression in the
template...

... which we didn't always do correctly. Teach
UnresolvedMemberExpr::getNamingClass() all about the new 
representation of injected-class-names in templates, so	that it	can
return a naming	class that is the current instantiation.

Also, when decomposing a template-id into its template name and its
arguments, be sure to set the naming class on the LookupResult
structure. 

Fixes PR6947 the right way.

llvm-svn: 102448