This fixes O_APPEND in direct IO mode.  Also checks writes against file size
limits, notably rlimits.

Reported by Greg Bruno.
Signed-off-by: NMiklos Szeredi <mszeredi@suse.cz>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>