autoconf does versioning strangely.  rather than actually tag releases, for the
last eight years the development team has constructed version strings by adding
the number of commits since the 2.69 version release as a prerelease tag.
(e.g., 2.69-100 would indicate the 100th commit since the v2.69 tag.)

the number of commits between the v2.69 tagged release and the git working
directory's head be calculated by running `git rev-list v2.69.. --count`.  the
autoconf development team has also included a script in the build-aux directory
that will calculate the official version tag: git-version-gen