* autoload.cc (MsgWaitForMultipleObjectsEx): Define.

	* autoload.cc (MsgWaitForMultipleObjectsEx): Define.
	(MsgWaitForMultipleObjects): Remove.
	* select.cc (select_stuff::wait): Use MsgWaitForMultipleObjectsEx with
	QS_ALLPOSTMESSAGE and, if possible, MWMO_INPUTAVAILABLE flags.  Explain
	why.  Fix a potential crash due to a NULL pointer in WAIT_FAILED case.
	(peek_windows): Use filter pattern on NT4.  Explain why.
	* wincap.h (wincaps::has_mwmo_inputavailable): New element.
	* wincap.cc: Implement above element throughout.