[PATCH, fortran] Fix numerous ICEs in IO statements with IOMSG

[FX]

> 2015-07-05  Steven G. Kargl  <kargl@gcc.gnu.org>
> 
> 	* io.c (check_char_variable): New function.
> 	(match_open_element, match_close_element, match_file_element,
> 	match_dt_element, match_inquire_element, match_wait_element): Use it.
> 
> 
> 2015-07-05  Steven G. Kargl  <kargl@gcc.gnu.org>
> 
> 	* gfortran.dg/iomsg_2.f90: New test.

OK to commit, thanks!

FX