Allowing the vncsession script to choose between multiple GNOME
configurations, with the initial use case being the Huygens
server. Currently, we can't NFS-mount the CVL's software server
onto the Huygens server's /usr directory, because our Huygens
license is currently locked to a "system ID" which depends on
running Huygens from the local disk (not an NFS share). But we
are still mounting the CVL's home directories on the Huygens
server, which means that without these modifications to the
vncsession script, Huygens users would end up with the CVL's
default panel menus which would be broken, because they would
refer to CVL software and menu files which don't exist on the
Huygens server.