* serial.h (gdb_pipe, serial_pipe): Declare.

	* serial.h (gdb_pipe, serial_pipe): Declare.
	* serial.c (serial_interface_lookup): Take a const char pointer.
	(serial_fdopen): Rename to ...
	(serial_fdopen_ops): ... this.  Add an OPS parameter and use it.
	Call the OPS' fdopen function if there is one.
	(serial_fdopen): Rewrite as wrapper to serial_fdopen_ops.
	(serial_pipe): New.
	(struct serial_ops) <fdopen>: New field.

	* ser-mingw.c (free_pipe_state):
	(free_pipe_state): Close output on non-pex pipes.
	(pipe_windows_fdopen): New.
	(gdb_pipe): New.
	(_initialize_ser_windows): Register pipe_windows_fdopen.
	* ser-go32.c (gdb_pipe): New.
	* ser-pipe.c (pipe_close): Close file descriptor even if there's
	no state pointer.
	(pipe_ops): Delete.
	(gdb_pipe): New.