USB patches

[Matthew Dillon]

    Well, we made a lot of stability fixes to USB that FreeBSD never had,
    and still doesn't.  We have to retain all of that work or we'd be going
    backwards.  In particular we made changes that allow USB devices to be
    pulled and plugged in willy nilly without crashing the machine, and
    that's an important feature.

    I think a more careful examination and incremental commit of the patch
    is in order.  I see some obvious improvements, but stuff is also missing.

    That said, the patches are only 160K each, it should be possible to audit
    them.

						-Matt