This usually happens when VS is building multiple projects at the same
time, hence running the prepare-script multiple times at once.

The shared approach results in conflicts if the generated class is used
in ATxCommon which is imported in the other projects. This way we can
use the symbols defined via ATxCommon in all depending projects.

The downside is that it slows down the build-process a bit as every
build from a project depending on ATxCommon (read: all others) will
change the generated code and thus force a re-build of ATxCommon and
the project itself. Since building the entire solution is still just
a matter of seconds, that's a fair trade-off.

Useful in combination with the AssemblyInformationalVersion property.

See https://stackoverflow.com/a/10334095/2018314 for details on sharing
resources among multiple projects in a solution.

The second colon (:) has strange effects in the "Output" window of
VisualStudio, messing up the text alignment.

There is no need to have this only as a post-build event, providing it
at this stage will allow us to include it in the assembly information.

Plus also check if the repository's commit state is dirty and report
accordingly.