[issue727] unloading sound driver panics box

[Matthew Dillon]

:actually it assumes so only in one place, the uaudio driver, and this is =
:even a bug which has been fixed in freebsd-7.  so i'd say let's sacrifice=
: uaudio (seems our only consumer didn't come back) and make the rest work=
: properly.
:
:cheers
:  simon

    The design of the audio stuff does not fill me with confidence.
    I really think we need to stick with high level locks just from
    a safety and kernel stability point of view, because snafus 
    will be a lot easier to debug.  Our spinlocks are simply not
    designed (on purpose) to handle large swaths of code.

						-Matt