[patch,fortran] Fix keyword check for specifiers (PR29452)

[FX Coudert]

>> 2006-10-26  Tobias Burnus  <burnus@net-b.de>
>>
>>     PR fortran/29452
>>     * io.c (check_io_constraints): Fix keyword string comparison.
>>
>> 2006-10-26  Tobias Burnus  <burnus@net-b.de>
>>
>>     PR fortran/29452
>>    * runtime/string.c (compare0): Check whether string lengths match.
>>
>> 2006-10-26  Tobias Burnus  <burnus@net-b.de>
>>
>>     PR fortran/29452
>>     * gfortran.dg/write_check.f90: Check run-time keyword checking.
>>     * gfortran.dg/write_check2.f90: Check compile-time keyword  
>> checking.

OK for the revised version. I think it should go into 4.2 too; can  
you regtest it and commit it there also?

FX