[PATCH] USB: Update Documentation/usb/URB.txt

This patch (as564) updates Documentation/usb/URB.txt, bringing it roughly
up to the current level.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>