It is better to run doc/Allwmake or doc/Doxygen/Allwmake and provide the
required options.

Patch contributed by Mattijs Janssens

- place under $WM_THIRD_PARTY_DIR/lib/$WM_OPTIONS
- relocate FOAM_MPI_LIBBIN accordingly

- solves problems that can occur when checking $PWD and links are involved

- also gives better isolation between scripts

- this improves the chances of having a current version

  * use $WM_THIRD_PARTY_DIR variable in top-level Allwmake
  * test new shell idiom for Allwmake files:
        # run from this directory only
        cd ${0%/*} || exit 1
    this might be especially useful when building optional components