This includes the following items:

 - a new wakeup feature: SMART_WAKE_CHILD (now unconditional) [this is a
   reworked version of the wakeup changes from Andrea's tree.]

 - scheduler parameter tunings (CHILD_PENALTY, MAX_TIMESLICE,
   STARVATION_LIMIT, MAX_SLEEP_AVG)

 - activate_task() splitup to separate the interactivity-active variant
   from the task-queue variant => this fixes our statistics in some cases.

 - finer-grained preemption: if priority is equal then the task with the
   longer pending timeslice wins.

 - make it possible to disable sync-wakeups via SYNC_WAKEUPS (default:1)

 - a naming cleanup (sleep_timestamp => last_run)

 - fix up STARVATION_LIMIT usage so that a value of 0 is recognized as 'no
   starvation limit'.

It also merges Linus' "priority boost backmerging"