Updated httpd config file to reflect new access controls introduced

on the Emulab web server.

Some notes:

 1) Public user web directories are now disabled
    - links from above the DocumentRoot to user devel trees must now be used.

 2) Internal access exceptions to production and devel directories are specified
    for the testbed root dir, and inherited by upper directories.
    - Simplifies configuration complextity

 3) External access to system (e.g., / /usr /var, etc) are disallowed now
    - Previously, symlinks could allow access to system directories.
    - Individual exceptions must be introducted when access to a specific
      directory is required.