futex: priority wakeup miss ordering

[Daniel Walker <dwalker@mvista.com>]

from commit ec92d08292d3e9b0823eba138a4564d2d39f25c7

The wakeup ordering should be in priority order. However if the priority
of a task is modified while it's waiting on the futex you will get an
out of order wakeup.

If you use a priority inheriting mutex this is correct. It's because the
rtmutex hooks into sched_setscheduler to catch any priority changes,
then re-queues with the new priority.. But the futex doesn't have this
hook.

Was this intentionally left out of this priority wake up patch? I
thought I would let you know in case you had a specific reason for not
handling this.. 

Daniel