Several fixes/changes:

* The unix group and gid are actuallt part of the group structure, not
  the project. So, when we load a project, load its default group as
  well, and have the routines for the name/gid hand off to the group.

* Change Lookup() to allow either a new idx or an old pid by looking
  at the format of the token. This will make it easier to transition
  to the new order of things.

* Part of the uncommitted uid changes is the addition of head_idx to
  replace head_uid. This code change is okay to commit now, since for
  the time being idx will shadow uid in all tables.