Rename cygWFMO to cygwait throughout and use the magic of polymorphism to "wait

Rename cygWFMO to cygwait throughout and use the magic of polymorphism to "wait
for stuff".
* fhandler.cc (fhandler_base_overlapped::wait_overlapped): Use simplified arg
form of cygwait.
* fhandler_console.cc (fhandler_console::read): Ditto.
* fhandler_audio.cc (fhandler_dev_dsp::Audio_out::waitforspac): Ditto.
(fhandler_dev_dsp::Audio_in::waitfordata): Ditto.
* fhandler_fifo.cc (fhandler_fifo::wait): Ditto.
* fhandler_serial.cc (fhandler_serial::raw_read): Ditto.
(fhandler_serial::raw_write): Ditto.
* select.cc (cygwin_select): Ditto.
* sigproc.h (cygwait): Rename from cygWFMO.  Define two argument and single
argument forms of this function.
* fhandler_tty.cc (fhandler_pty_slave::open): Use method to query if tty is
open.
(fhandler_pty_slave::read): Send SIGHUP when master is detected as closed.
(fhandler_pty_common::close): Close input_available_event in callers since
master may need to signal it first.
(fhandler_pty_master::close): Lie and set input_available_event when closing,
then close input_available_event.
(fhandler_pty_slave::close): Close input_available_event explicitly here.
* tty.h (tty::is_master_closed): Declare new method.