I realized having the revision as a build number is the wrong idea as it
implies packagers will have to rebuild GIMP for just a revision. Yet
very often revision may just be data change or dependency fix/update
without rebuild needed (i.e. no ABI change).
Instead let's keep this package information as a file 'gimp-release'
(inspired by /etc/os-release and other /etc/*-release files of
distributions).
(cherry picked from commit 87e9ebcfad)
Since commit 9fdf35550b, I removed the GIMP_APP_GLUE_COMPILATION check
because we need to have the whole versioning info from the new debug
widget. It just makes sense to go further and just make this a proper
internal API to get version information.
