re PR c++/17232 ([DR 1640] classes and class template specializations treated differently w.r.t. core issue #337)

	PR c++/17232
	PR c++/56642
	* pt.c (tsubst_decl): Check return value of register_specialization.
	* typeck2.c (abstract_virtuals_error_sfinae): Re-apply complete_type
	change.

From-SVN: r196849