Distribute also the generated control.rng file, the reason is that "trang" is a Java tool which adds huge dependency in OBS.
The conversion needs to be done manually (by running "rake generate_rng") and the converted RNG file must be committed to Git.
At build time the RNG file from tarball will have a newer time stamp and thus it will not need rebuild/update making "trang" unnecessary.
See also the documentation for the control file.