Whichever license you plan to use, the process involves adding two elements to each source file of your program: a copyright notice (such as ÔÇ£Copyright 1999 Terry JonesÔÇØ), and a statement of copying permission, saying that the program is distributed under the terms of the GNU General Public License (or the Lesser GPL).
This, together with the idea of the header to be a thing that can easily change (eg. someone using our code, he has to use our header or parts of it and will add stuff), i came up with:
Copyright 2010 John Doe <firstname.lastname@example.org>
This file is part of the Spring RTS game engine,
and is licensed under the GNU GPL v2 and later.
See the file README.LICENSE for details.
As i got it, we have to include a legal person to hold the copyright,
and i guess the Spring community is not one, so we have to use our individual names.
README.LICENSE currently contains GPLv2 in .txt format. i would like to move it to either gpl-2.0.txt or Documentation/gpl-2.0.txt, add the same for v3, and then only link to these to files from within README.LICENSE.
i plan to make a branch with the transition to the new header (plus other related stuff, eg. as explained in here). once the transition is done, changing the header would be simple of course, but the initial enforcement will need lots of hand tweaking: is there a header already? if yes, what info of it is still needed, ...