This is a port of work Ben LaHaise did around 2.5.20 time.  I split it
up and updated it for the new preempt_count semantics.

* clean thread info infrastructure (1/3)
    - take out all instances of things like (8191&esp) to get
      current stack address.

Has a few unused things that will be used in the following two patches.
-- 
Dave Hansen
haveblue@us.ibm.com