app: fix abbreviated commit hashes
The abbreviated commit hash we show in the shell and the about dialog is currently just the last 7 characters of 'git describe', based on the assumption that abbreviated hashes are always 7-digits long. When the hash is longer than that, we're just showing a nonsense commit. This was never a good idea, since users can override this, and since disambiguation can result in longer hashes, but since git 2.11, the default abbreviated hash length is determined based on the size of the repository, which currently results in 10 digits for us. Let's just do it right.
Showing with 7 additions and 14 deletions