Hello Sven,
Afterwards the development branch should change the RELEASE_VERSION to the upcoming version number and the EXTRA_VERSION to a string which informs the user that it is "unstable" and in development. This could be for example "-dev", "-pre-alpha", "-beta" or "-rc1".
I like your patch a lot. It could solve a nasty little problem that always tends to be forgotten. :-)
Unfortunately, our compile farm which feeds the package repository extracts the SOURCE_VERSION from batman.h to generate the package name. Unless we rewrite the compile scripts to extract both defines we can't apply your patch as-is. This rewrite is not as painless as it could be. Certainly, at some point we want to touch the scripts to optimize the speed but that wasn't on our agenda right now.
Do you see alternatives which allow us to reuse the existing compile farm and have the functionality you implemented ?
Regards, Marek