Support for 'template' as a disambiguator (PR7030)

    ParseOptionalCXXScopeSpecifier() only annotates the subset of
    template-ids which are not subject to lexical ambiguity. Add support
    for the more general case in ParseUnqualifiedId() to handle cases
    such as A::template B().

    Also improve some diagnostic locations.

Fixes PR7030, from Alp Toker!

llvm-svn: 103081