It gets tiresome to rebuild the project everytime one makes changes to
any of the unit tests. We don't likely publish results based on the
debug code anyway, so tracking the version number there is not such a
pressing issue.
Otherwise, the library may be declared "done" before the version number
process have had any change to touch files it depends upon. This ensures
that the version number is correct before we start building the library.
Akin to config.h, we write project-version.h whenever the VCS sha hash
of the project changes. This file can then be included to embed this
into the project. Since this changes more frequently, we choose another
file than config.h. Care is also taken to not rewrite the header if the
information doesn't change, but the project is rebuilt.
