Pull UBIFS updates from Artem Bityutskiy:

 - Added another debugfs knob for forcing UBIFS R/O mode without
   flushing caches or finishing commit or any other I/O operation.  I've
   originally added this knob in order to reproduce the free space fixup
   bug (see commit c6727932: "UBIFS: fix a bug in empty space
   fix-up") on nandsim.

   Without this knob I would have to do real power-cuts, which would
   make debugging much harder.  Then I've decided to keep this knob
   because it is also useful for UBIFS power-cut recovery end
   error-paths testing.

 - Well-spotted fix from Julia.  This bug did not cause real troubles
   for UBIFS, but nevertheless it could cause issues for someone trying
   to modify the orphans handling code.  Kudos to coccinelle!

 - Minor cleanups.

* tag 'upstream-3.6-rc1' of git://git.infradead.org/linux-ubifs:
  UBIFS: remove invalid reference to list iterator variable
  UBIFS: simplify reply code a bit
  UBIFS: add debugfs knob to switch to R/O mode
  UBIFS: fix compilation warning