Thanks to Adriaan Vuik for reporting.

Thanks to Bernard van Heck for reporting.

Thanks to Bas Nijholt for reporting this.

allow attaching a lead to a builder that contains sites that are not commensurate with the leads's symmetry

* Only extract the version from Git when the top level directory of the Git
  repository coincides with the root directory of the Kwant distribution

* Disregard tags on branches that were merged-in (with Git >= 1.8.4).