io.c (check_io_constraints): Don't look at dt->advance->value.charater.string, unless it is a CHARACTER constant.

	* io.c (check_io_constraints): Don't look at
	dt->advance->value.charater.string, unless it is a CHARACTER
	constant.

	* gfortran.dg/advance_2.f90: New test.
	* gfortran.dg/advance_3.f90: New test.

From-SVN: r112417