Change default version to 4.1.0 (may need to revert to 4.0.1 after
further testing of 4.1.0)

The default ParaView is now 4.0.1 pending completion of testing of 4.1.0

- otherwise there is actually no means of placing a site-site
  prefs.sh in the $WM_PROJECT_SITE/ directory

- leave bashrc/cshrc and prefs.{csh,sh} in etc/ for visibility

- use standard *.sh, *.csh endings

- need to trap possibly weird input within etc/bashrc, etc/cshrc and
  can't easily redirect stderr in csh.

- avoid editing of settings.{sh,csh}

This reverts commit c5bea524.

- this change was wished by Mattijs and/or Henry

- allow command-line settings to retain the flexibility of 'foamPV'
  alias mechanism.

This reverts commit 2e1e671d.

- drop FOAM_MPI_LIBBIN variable in favour of FOAM_MPI from which
  two different locations can be determined.

  Previously there was something like this:

      FOAM_MPI_LIBBIN = $FOAM_LIBBIN/openmpi-1.5.1

  We now instead determine the locations from the FOAM_MPI directly:

      FOAM_MPI=openmpi-1.5.1

          $FOAM_LIBBIN/$FOAM_MPI     -> OpenFOAM  mpi-related
          $FOAM_EXT_LIBBIN/$FOAM_MPI -> ThirdPary mpi-related

ENH: relocate ParaView libraries and plugins back under FOAM_LIBBIN

- as discussed with Mattijs