* Per the Developer's meeting today, restructure the threading in Open MPI a bit
more:
  - Remove OPAL_ENABLE_MULTI_THREADS, since it didn't really do anything
    correctly.  Opal always has threads enabled at this point.
  - Remove OMPI_ENABLE_PROGRESS_THREADS, since this hasn't worked in
    8 years and it has performance issues we'll never be able to
    overcome.  Note that we have plans for re-adding async progress, using
    a hybrid protocol of async and sync sends.
  - OMPI_ENABLE_THREAD_MULTIPLE now determines whether the thread lock
    macros do the check or not.
  - Condition variables are ALWAYS polling right now, which fixes the thread
    live-lock currently found when THREAD_MULTIPLE is turned on.