- experienced while reusing src/Pstream/Allwmake-mpi to create
  additional mpi-layers after installation. Since the copied sources
  are not located within the OpenFOAM source-tree (and/or the
  source-tree is non-writable), it should not and does not use the
  central build/WM_OPTIONS directory.

  However, when exploring for the appropriate local Make directory, it
  searched for the current '.' directory instead of checking for the
  resolved directory.

  This fails, since there is no src/Pstream/Make directory.
  Must check for src/Pstream/mpi/Make directory first!

- Adjust wclean to always remove a local build directory
  (Make/WM_OPTIONS) for additional safety.
  After which, attempt to remove central build/WM_OPTIONS version too.