sympa-upgrade-password: provide a way to save progress

[taggart]

Expected Behavior

It would be nice if sympa-upgrade-password either saved it's progress periodically, or supported saving upon interruption.

Current Behavior

Currently if I interrupt the process after some time, the cache does not get saved and all work is lost.

Possible Solution

Options I thought of:

• save the cache after each successful password_user conversion. This is kind of a lot but would also let you watch the cache grow and check status.
• setup a signal handler so upon interrupt or hangup it saves the current progress

Context

I have 140k users with RC4 passwords to convert, so it will probably take a while :)
But the target audience for this feature is pretty small.

Bonus feature request: the --limit option isn't documented

[taggart]

It turned out that even with 140k users I just didn't interrupt it and it still finished overnight. The feature would still be nice, but the number of the users using this tool is approaching zero (maybe I am the last one!)