Updated Chapter 2, Section 3.2 of the Admin Guide

Updated Chapter 2, Section 3.2 of the Admin Guide

Removed the reference to the Authentication Server and added a reference to the Kerberos Server and Kerberos 5 authentication for foreign clients.

Replaced AFS Product Support with the AFS registrar as the maintainer of the
public CellServDB file. A link was added to grand.central.org for getting the
latest copy of the file and submitting changes for the local site.

Reviewed-on: http://gerrit.openafs.org/379
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>