PR c++/20332
	PR c++/21631
	* call.c (reference_binding): Treat lvalue/rvalue mismatch and
	dropped cv-quals as a bad conversion.
	(convert_like_real) [ck_ref_bind]: Explain them.
	(compare_ics): Check badness before stripping reference
	bindings.  Handle comparing bad reference bindings.
	* typeck.c (comp_cv_qualification): Add overload that just takes
	integers.
	* cp-tree.h: Declare it.

From-SVN: r210436