OS X fixes:

  * Applied Eugenio's fix to the DVDioctl driver. I didn't test it, but
    it should not hang the kernel anymore.

  * Ported most dvd_ioctl.c functions to the DVDioctl driver: ReportAgid,
    ReportChallenge, ReportKey1, ReportASF, InvalidateAgid, SendChallenge,
    SendKey2. They should comply with the "Mt. Fuji Commands for Multimedia
    Devices" paper.

    Last remaining problem: ReadCopyright and ReadKey. The version of
 Darwin I have here only has reportKey() and sendKey() functions in
 the IODVDBlockStorageDevice class (pages 413 and 449 of the Mt. Fuji
 paper), but we also need the READ_STRUCTURE (page 357) which I couldn't
 find anywhere in the kernel headers. Either I missed it, or we'll have
 to wait for Apple to implement it (or maybe we can emulate this command
 with some other IOKit commands).