aufs: bugfix, pinning in mvdown

Unlike copy-down, move-down has to unlink the whiteout or the real entry
on the upper branch. So one more dir->i_mutex lock is necessary.

Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>
aufs: minor optimization, stop notifying

When the branch it at the bottom of fhsm-ed branches, stop notifying FHSM.

Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>
aufs: tiny, remove an obsoleted comment

Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>
aufs: tiny, refine debugging in mvdown

Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>
Merge remote-tracking branch 'aufs3-standalone/aufs3.9/00base' into aufs3.9/10static
Merge branch 'aufs3.9/10static' into aufs3.9/11proc_map
Merge branch 'aufs3.9/11proc_map' into aufs3.9/18public