Fix two FreeBSD build issues related to libusb-1.0.

FreeBSD's libusb-1.0 compatible library has a few differences compared
to the "normal" libusb-1.0 from libusb.org which we have to work around.

LIBUSB_CLASS_APPLICATION doesn't exist in FreeBSD's libusb, and
libusb_handle_events_timeout_completed() doesn't exist either.
The latter is basically libusb_handle_events_timeout() with an extra
(unused by us) parameter, so the workaround is relatively simple.

This fixes bug #185.