- pass through normal paraview (double-dashed) options

- bypass the plugins logic when the --data=... option is provided.
  This allows the command 'paraFoam --data=...' to work too.

- requested by Mattijs, this allows the developer to provide some
  default options, or otherwise adjust the logic.

- the following set/unset operations are disallowed (FatalError)
  * changing -case, -roots, -parallel
  * changing type (bool <-> non-bool)
  * no mpi options

- 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

This does not change the form of the function but the coefficients must be set appropriately.