Faster node/fork/MPI distribution for External mode. This changes the
session file format so it will be incompatible, so until we get that
sorted out it's ifdef'ed out and we use the core scheme.
Merge branch 'bleeding-jumbo' into bleeding-mask

* bleeding-jumbo:
  Faster node/fork/MPI distribution for External mode. This changes the session file format so it will be incompatible, so until we get that sorted out it's ifdef'ed out and we use the core scheme.