re PR c++/47080 ([C++0x] explicit conversion function return conversions not restricted to qualifications)

	PR c++/47080
	* call.c (rejection_reason_code): Add rr_explicit_conversion.
	(print_z_candidate): Handle it.
	(explicit_conversion_rejection): New.
	(build_user_type_conversion_1): Reject an explicit conversion
	function that requires more than a qualification conversion.

From-SVN: r175217