Reimplement the comparison of a class template partial

specialization's template arguments against the primary template's
template arguments using the obvious, correct method of checking the
injected-class-name type (C++ [temp.class.spec]p9b3). The previous
incarnation of this comparison attempted to use its own formulation of
the injected-class-name, which is redudant and, with the introduction
of variadic templates, became wrong (again).

llvm-svn: 122508