2011-05-04  Marc Glisse  <marc.glisse@normalesup.org>

	PR libstdc++/47913 (again)
	* include/std/ratio (ratio_add, ratio_less): Rewrite.
	* testsuite/20_util/ratio/operations/47913.cc: Extend.
	* testsuite/20_util/ratio/cons/cons_overflow_neg.cc: Adjust dg-error
	line numbers.
	* testsuite/20_util/ratio/operations/ops_overflow_neg.cc: Likewise.