WIP
    
    mpich enabled
    
    - shell scripts need to be updated to refer to the _mpich suffixed
      binaries etc.
    - bits in mpich/share need to be checked if they can be moved to a
      common sub-package: some of these are hard coded and may be far too
      much work: needs looking into.
    
    It seems to hard code the path to cleanup, for example. Not quite sure
    how to tweak that.