First part for thread help with respect to scheduling decisions

[Sebastian Huber]

Some SMP locking protocols like MrsP use a help out mechanism for threads.
This patch set adds the ability to indicate the need for help.  Threads in need
for help are displaced threads and threads which cannot change into the
scheduled state after an unblock operation.

A displaced thread is a thread that encounters a scheduler state change from
scheduled to ready.  Such a displaced thread can ask threads which depend on
resources owned by the displaced thread for help.
    
In case the unblock operation returns no displaced thread, then this
indicates that the unblocked thread is now in the ready state and has no
processor allocated.  Such a thread can ask now also for help.

The second part will add a new scheduler operation to try to provide help if
requested.