Change .chpass <bot> to allow easy setting of strong random passwds

[michaelortmann]

Bot-Link-Passwords should be strong. We should try to make it easy to set strong ones. Esp. since our MD5 challenge–response authentication isn't that secure anymore.

I propose to make .chpass <bot> r set a such a pwd.

r as a magic char is possible here, because r is not a valid password (too short).

Maybe its also interesting for .chpass <user>.