Speedup of calc_release_version.py (#1383)

* Cleaner argument handling and type-checking in calc_release_version
* Speedup of calc_release_version by minimizing subprocesses

Instead of continually asking Git whether a particular commit hash is
pointed-to by a given tag, ask Git upfront for a mapping between all
commit hashes and the associated tags. Then, look for the commit in
the mapping as a single step.