[patch] fix PR libfortran/20179

[FX Coudert]

> 2005-09-11  Francois-Xavier Coudert  <coudert@clipper.ens.fr>
> 
> 	PR libfortran/20179
> 	* io/unix.c (is_preconnected): Add function to test if a stream
> 	corresponds to a preconnected unit.
> 	* io/io.h: Add prototype for is_preconnected.
> 	* io/transfer.c (data_transfer_init): Do not truncate
> 	preconnected units.

Committed on mainline. Committed on 4.0 along with the patch for PR 
libfortran/19872 (which was never committed) and a testcase for this PR 
(which was neither committed on 4.0 nor on mainline). Committed the 
testcase for PR19872 to mainline too, thus :)

2005-09-11  Francois-Xavier Coudert  <coudert@clipper.ens.fr>

         PR libfortran/19872
         * gfortran.dg/overwrite_1.f: New test.

2005-09-11  Francois-Xavier Coudert  <coudert@clipper.ens.fr>

         PR libfortran/19872
         PR libfortran/20179
         * io/unix.c (is_preconnected): Add function to test if a stream
         corresponds to a preconnected unit.
         * io/io.h: Add prototype for is_preconnected.
         * io/transfer.c (data_transfer_init): Truncate overwritten files
         on first write, but not preconnected units.