Panic with USB2 release candidate

[Thomas Sparrevohn]

I downloaded the release candidate 2 for the new USB stack and while it work very well for most things 
I am getting repeated panics when using heavy disk traffic - I believe the issue is related to the 
problems I described in the "out of bounce buffers mail" - Yet with the new stack it show up
correctly in the USB UMASS dma code as a fault

Anyhow its a pretty nasty panic - I have a number of core dumps if its of any use