add_listed()
  Add one record into SQL list for a policy.
  
  Usage: add_listed(dbc, flags, expire, table, scanners)
  
  Where: dbc is an database connection
         flags is an string, which defines what and where to add. It can be:
             BA - to blacklist sender's IP address
             BS - to blacklist sender's email address
             BR - to blacklist recipients
             WA - to whitelist sender's IP address
             WS - to whitelist sender's email address
             WR - to whitelist recipients
         expire is an integer, which defines validity of a new record
           in seconds. Set it to -1 for infinite time.
         table can define table alternative
  
  Example: add_listed(db.sqlite(), 'BA', -1, 'greylist', b2f(libclam()))
  
  New in version 0.8.0.