Allow summarisation of commits that have not been backed up
by infinitepush.
- Add a template keyword (backupstatus) which evaluates to one of "Public", "Backed up", "Backup pending", or "Not backed up" depending on the backup state of the commit. Commits are pending for 10 minutes, after which they are declared not backed up.
- Add a summary to the end of smartlog that shows the number of commits that are not backed up.
Configuration options allow the addition of an education message to inform users what to do about their failing backups, and the message can also be suppressed.
According to a recent discussion, we prefer suppress-summary style config names.