hotplug cpu: PATCHes for 3 issues

[cpw@sgi.com (Cliff Wickman)]

In the 2.6.21 kernel there are still 3 hotplug issues that are cpuset-
related, and that I find to still be problems.   And for which I offer
patches.

These have been submitted before, and subsequently cleaned up per
comments received.  I'm resubmitting all 3 for consideration and further
comment.

1)  [PATCH 1/1] hotplug cpu: cpusets/sched_domain reconciliation
2)  [PATCH 1/1] hotplug cpu: move tasks in empty cpusets to parent
3)  [PATCH 1/1] hotplug cpu: migrate a task within its cpuset

1) Reconciles cpusets and sched_domains that get out of sync
   due to hotplug disabling and re-enabling of cpu's.
   Tasks can get into infinite hangs without this fix.
     kernel/cpuset.c
     kernel/sched.c 

2) When a cpuset is emptied by disabling its cpus, move tasks to 
   a parent cpuset.
   This is a correction of the current procedure, which moves such
   tasks to the wrong cpuset.
     kernel/cpuset.c

3) Causes a task running on a disabled cpu to migrate to a cpu within
   its cpuset.
   This behavior is particularly important for a NUMA system on which
   tasks have been explicitly placed.
     kernel/sched.c