Flight Gear now has an anonymous CVS repository.  Currently, it is read
only, but it will allow you to maintain your own absolutely up to date
source tree.  You will also be able to do diffs, extract older versions
of files, and all the other fancy CVS stuff.

Instructions for accessing the FG cvs repository can be found by 
following the "CVS Resources" link from the main FG web page:

    http://www.menet.umn.edu/~curt/fgfs/