more MFCs to RELENG_4

[Julian Elischer]

You'll find a diff at:

http://www.freebsd.org/~julian/usb-4.diff

This merges a lot of the USB infrastructure.
I was amazed how little changing had to be done
to allow this to work on 4.x.

The files become almost teh same as on -current.
(minus small changes here and there)

if you use USB on 4.x, please check this out and let me know if I have 
broken
anything.

Especially try mistreating it (if it takes such mistreatment in 4.x
at the moment) to see if we've broken error handling etc.

I'll commit this in a day or so and keep going.. hubs next I think.