ext4: mark all metadata I/O with REQ_META

As Dave Chinner pointed out at the 2013 LSF/MM workshop, it's
important that metadata I/O requests are marked as such to avoid
priority inversions caused by I/O bandwidth throttling.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

diff --cc fs/ext4/balloc.c
Simple merge

diff --cc fs/ext4/ialloc.c
Simple merge

diff --cc fs/ext4/mmp.c
Simple merge

diff --cc fs/ext4/super.c
Simple merge