is check if semaphore is actually locked, which can be trivially done in
portable way. Code gets more reabable, while we are at it... 

SGI-PV: 953915
SGI-Modid: xfs-linux-melb:xfs-kern:26274a
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Nathan Scott <nathans@sgi.com>