MPI documentation: We can now start a session with MPI and resume it with
-fork, or the other way round.
MPI: Ensure that a resumed session runs on the correct number of nodes.
Merge branch 'bleeding-jumbo' into memdbg

* bleeding-jumbo:
  MPI: Ensure that a resumed session runs on the correct number of nodes.
  MPI documentation: We can now start a session with MPI and resume it with -fork, or the other way round.