autoconf now executes "git describe" to know which version is going to
build. The version depends on the latest git tag (see howto_new_release.txt).

There are two versions: the AssemblyVersion (which is like 1.6.2, since
it only accepts this format) and the new buildInfo.chronojumpVersion and
buildInfo.chronojumpLastCommitTimestamp (not used at the moment).

The buildInfo.chronojumpVersion is used as display string: it's like
1.6.2 if it's a build from a tag or
1.6.2-number_of_commits_since_last_tag-commit_hash. This way we can
identify the build uniquely even if it was from a specific branch.