* cp-tree.h (hash_tree_cons_simple): New macro.
	* pt.c (tsubst_arg_types): New function.  Use hash_tree_cons.
	(coerce_template_parms): Use make_temp_vec, instead of
	make_tree_vec.  Document this behavior.
	(lookup_template_class): Likewise.
	(tsubst, cases METHOD_TYPE, FUNCTION_TYPE): Use tsubst_arg_types.
	Remove dead code (and add ssertion to check its deadness).  Fix
	bug w.r.t. exception specifications.

From-SVN: r22233