Throughout, use user32 UNICODE functions rather than ANSI functions.

	Throughout, use user32 UNICODE functions rather than ANSI functions.
	* autoload.cc: Convert all definitions for ANSI user32 functions to
	definitions for the corresponding UNICODE function.
	(SendMessageA): Remove.
	(SendNotifyMessageW): Define.
	* fhandler_windows.cc (fhandler_windows::write): Use SendNotifyMessageW
	call rather than SendMessage to make function always return immediately.
	(fhandler_windows::read): Make function interruptible and a cancellation
	point.  Handle O_NONBLOCK.
	* select.cc (peek_serial): Don't wait for signal_arrived here.
	* window.cc (wininfo::winthread): Call CreateWindowExW directly rather
	than CreateWindow wrapper.