posix_lock_file() always allocates new locks in advance, even if it's easy to
determine that no allocations will be needed.

Optimize these cases:

 - FL_ACCESS flag is set

 - Unlocking the whole range
Signed-off-by: NMiklos Szeredi <miklos@szeredi.hu>
Cc: Trond Myklebust <trond.myklebust@fys.uio.no>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>