- foamExec was removed as part of commit 6c68c34e1a but
overlooked the fact that it is partly still needed by foamJob.
When running in parallel, it is used to source the etc/bashrc env.
Reinstated a stripped down form, which has been relocated to
bin/tools directory (it should not be directly called by the user).
The previous version switching functionality has nonetheless be
dropped since it only worked only when a rigid naming convention for
OpenFOAM installations was followed.
ENH: add foamJob log=, -log-app, -no-log options, improved coding quality
