* fhandler.h (class fhandler_netdrive): Add method rewinddir.

	* fhandler.h (class fhandler_netdrive): Add method rewinddir.
	* fhandler_netdrive.cc (struct netdriveinf): New structure to
	store thread arguments.
	(thread_netdrive): Thread handling all potentially blocking
	WNet... calls.
	(create_thread_and_wait): Start and wait for above thread.
	(fhandler_netdrive::exists): Change to call create_thread_and_wait
	instead of calling WNet... function.
	(fhandler_netdrive::readdir): Ditto.  Fix error handling.
	(fhandler_netdrive::rewinddir): New method.