I've posted all these before, the only notable change is
treating that one gphoto2 case as warn-and-continue rather
than return-with-failure.


usb_set_configuration() cleanup

 * Remove it from the USB kernel driver API.  No drivers need it now,
   and the sysadmin can change bConfigurationValue using sysfs (say,
   when hotplugging an otherwise problematic device).

 * Simpler/cleaner locking:  caller must own dev->serialize.

 * Access from usbfs now uses usb_reset_configuration() sometimes,
   preventing sysfs thrash, and warns about some dangerous usage
   (which gphoto2 and other programs may be relying on).  (This is
   from Alan Stern, but I morphed an error return into a warning.)

 * Prevent a couple potential "no configuration" oopses. (Alan's?)

 * Remove one broken call from usbcore,  in the "device morphed" path
   of usb_reset_device().  This should be more polite now, hanging
   that one device rather than khubd.