Requiring a certain license is just a stupid thing to begin with. The requirement should be that it's free (or you can add the extra requirement that it should be GPL-compatible like gna.org has, that's also useful because you then share all code).
The GFDL is a free license, so your comment makes no sense. Savannah only allows for free licenses, a perfectly valid requirement.
But if somebody wants to release his documentation under the BSD license, I don't see any reason why that should be forbidden by savannah.
It isn't forbidden on Savannah, it is explcitly allowed.
Cheers.