This patch does the following:
(o) Add comments showing what needs to be done to complete the hot-unplug
    system.
(o) Add a BUG_ON() for (what is now) a critical failure case.
(o) Make certain that a debug print happens even if a usb_get_intfdata()
    crashes.
(o) Add an un-necessary up() to balance a down, for the auto-code-checkers.