Include git lightweight tags for version detection

[git-developer]

GitVersion.cmake uses git describe to detect the application version.

By default, Git reads only annotated tags. The git repo currently contains a few version tags, but they're all lighweight tags, none of them is annotated. Thus, the version detection fails and the resulting version (mbpoll -V) is always 1.0-0.

Git may be advised to handle lightweight tags by setting the argument --tags. This results in a proper version, e.g. 1.4-11 for the current master branch (1968de6).

[git-developer]

@epsilonrt Do you see a chance to look at this PR?