Hacks to make pgm work on litmus. will clean up...

1) Ensure spinlock holder cannot be preempted
   in order to avoid possible deadlock (esp.
   on uniprocessor/partitioned).
2) Disable phased periods. (Use was probably
   technically incorrect w.r.t. Liu's analysis.)
3) Only generate graph directory if FIFOs are
   in use.
4) pgmrt: Generate a unique name for the graph
   data file.
5) pgmrt: Prevent internal nodes from bailing
   out early due to duration overrun. Limit
   this ability to src nodes.