type_traits (result_of): Fix handling of cv-quals.

	* include/std/type_traits (result_of): Fix handling of cv-quals.
	* testsuite/20_util/result_of/1.cc: New.
	* testsuite/20_util/result_of/2.cc: New.
	* testsuite/20_util/declval/requirements/1_neg.cc: Adjust dg-error
	line numbers.
	* testsuite/20_util/make_signed/requirements/typedefs_neg.cc:
	Likewise.
	* testsuite/20_util/make_unsigned/requirements/typedefs_neg.cc:
	Likewise.

From-SVN: r185845