PR 15068

PR 15068
	* utils.c (quit): Call SERIAL_DRAIN_OUTPUT rather than
 	SERIAL_FLUSH_OUTPUT.
	* serial.h (struct serial_ops): Add drain_output, pointer to
 	function that waits for output to drain.
	(SERIAL_DRAIN_OUTPUT): Macro to wait for output to drain.
	* ser-unix.c (hardwire_drain_output): New function and prototype.

	* ser-unix.c (hardwire_ops): Add entry for drain_output function.
	* ser-tcp.c (tcp_ops): Ditto.
	* ser-ocd.c (ocd_ops): Ditto.
	* ser-mac.c (mac_ops): Ditto.
	* ser-go32.c (dos_ops): Ditto.
	* ser-e7kpc.c (e7000pc_ops): Ditto.