Commands to review/fix:
 * Dummy commands, right now they just reply with a "O ok", but probably they
   should do something:
   - FSET (actually it stores the flags as specified by the client, so they
     could be retrieved later by FGET, but we don't do things with them).
 * Not yet implemented commands:
   - CLEAR
   - RESET
   - PURGE
   - PREVIOUS_MODULE
     (this one is not documented in the debconf protocol specs, as well as DATA
     and PROGRESS, wtf?)
