* errno.cc (errmap): Handle ERROR_IO_PENDING.

* fhandler.cc (fhandler_base::open): Make tape I/O asynchronous.
	* fhandler.h (class fhandler_dev_tape): Add mt_evt member.
	* fhandler_tape.cc (mtinfo_drive::initialize): Initialize async_writes.
	(mtinfo_drive::close): Handle async writes.
	(mtinfo_drive::read): Add mt_evt parameter.  Use overlapped I/O.
	(mtinfo_drive::async_wait): New function.
	(mtinfo_drive::write): Add mt_evt parameter.  Use overlapped I/O.
	Handle async writes.
	(mtinfo_drive::_set_pos): Handle async writes.
	(mtinfo_drive::set_partition): Ditto.
	(mtinfo_drive::prepare): Ditto.
	(mtinfo_drive::get_status): Drop useless "else".  Handle async_writes
	flag.
	(mtinfo_drive::set_options): Handle async_writes flags.
	(fhandler_dev_tape::close): Close mt_evt handle.
	(fhandler_dev_tape::raw_read): Create mt_evt handle and use in call
	to mtinfo_drive::read.
	(fhandler_dev_tape::raw_write): Create mt_evt handle and use in call
	to mtinfo_drive::write.
	* mtinfo.h (MTINFO_VERSION): Bump.
	(enum dirty_state): Add async_write_pending state.
	(class mtinfo_drive): Add OVERLAPPED struct "ov".  Add async_writes
	flag.
	(mtinfo_drive::async_wait): Add declaration.
	(mtinfo_drive::read): Add mt_evt parameter.
	(mtinfo_drive::write): Ditto.

	* registry.cc (load_registry_hive): Call enable_restore_privilege
	instead of set_process_privilege.

winsup/cygwin/fhandler.h

@@ -535,6 +535,7 @@ class fhandler_dev_floppy: public fhandler_dev_raw
 class fhandler_dev_tape: public fhandler_dev_raw
 {
   HANDLE mt_mtx;
+  HANDLE mt_evt;
 
   bool is_rewind_device () { return get_minor () < 128; }
   unsigned int driveno () { return (unsigned int) get_minor () & 0x7f; }