When checking for the necessary 'template<>' headers based on the

nested of an out-of-line declaration, only require a 'template<>'
header for each enclosing class template that hasn't been previously
specialized; previously, we were requiring 'template<>' for enclosing
class templates and members of class templates that hadn't been
previously specialized. Fixes <rdar://problem/9422013>.

llvm-svn: 131207