* pt.c (tsubst): Decrease the template-level of
	 TEMPLATE_TEMPLATE_PARMS.  Likewise for the DECL_INITIAL of a
	 TEMPLATE_PARM_INDEX.
	 (template_decl_level): New function.
	 (unify): Make sure to record unifications for template
	 parameters, even when the parameters exactly match the arguments.
	 Combine duplicated code for TEMPLATE_TEMPLATE_PARMs and
	 TEMPLATE_TYPE_PARMS.  Don't try to unify template parameters that
	 aren't from the level we're currently working on.

From-SVN: r19378