* 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
