Currently rpstir-upgrade requires the user to specify the previous version as a command-line argument. This should be unnecessary; it should auto-detect the previous version.

This can be done by saving the version number in a file or database row somewhere and updating it when rpstir-upgrade is done. (If the saved version number is missing, then rpstir-upgrade can require the user to specify the previous version.)

Reported by: rhansen

Original Ticket: rpstir/tickets/17