Cleaning up the mess with the re-released 5.1a with the 6.0 license (TrueCrypt Collective License Version 1.4; TrueCrypt License Version 2.5). See note in previous commit message.
Amazingly found .sig file for original 5.1a release at: http://downtown.trilo.de/svn/downloads-20080102/trunk/_20080424-2041_truecrypt-5-1a_/