load_trees

  ========================================================================
  USAGE : load_trees myfile.tdt [my_database]

        If my_database is given it must be fully defined as
        database%dbpass@host:service:user%userpass
        e.g.
        test%executive_pw@vcs:thor:johnb%
        The default is to update VCS@vcs

  The input myfile.tdt will usually have come from conversion of an MDL
  SD file using build_trees().

  ========================================================================