Use CVS $Id$ tags in your files

For configuration files that support comments, like rc.local, add "# $Id$" to the top of the file.  This expands to:
 #$Id: rc.local,v 1.8 2008/03/24 14:49:30 merdely Exp $

This CVS $Id$ tag allows you to easily compare versions and see when it was last checked in.