* fhandler.h (class fhandler_serial): Declare switch_modem_lines.
* fhandler_serial.cc (fhandler_serial::switch_modem_lines): New
static function to set or clear DTR and/or RTS.
(fhandler_serial::ioctl): Use switch_modem_lines for TIOCMSET
and new TIOCMBIS and TIOCMBIC.
* include/cygwin/version.h: Bump API minor number.