This is a revision of my earlier patch to make
stderr output from program run with

   target remote | some_program

to be routed through gdb_stderr, so that MI
frontend sees that output.

The original patch is at:

	http://thread.gmane.org/gmane.comp.gdb.patches/32540

and this version differs by not having any #ifdef WIN32 inside
ser-base.c, but instead using new method in 'struct serial_ops',
that is initialized in ser-mingw.c.

OK?

- Volodya