log()
  Advanced logger interscanner.
  
  This scanner can be used to log some special data.
  You can use these variables in format string:
    %(LEVEL)s           - detected virus level
    %(VIRNAME)s         - name of detected virus, empty if CLEAN
    %(STATUS)s          - if mail is dropped, rejected, ...
    %(QNAME)s           - quarantine file name
    %(SCANNER_NAME)s    - scanner which reported this virus
    %(SENDER)s          - scanned message sender
    %(RECIPIENTS)s      - scanned message recipients
    %(RECIPIENT)s       - scanned message recipients one by one (only for SQL)
    %(SUBJECT)s         - message's header Subject
    %(SIZE)s            - email size
    %(VERSION)s         - sagator's version
    %(SENTBY_IP)s       - sender's IP
    %(SENTBY_NAME)s     - sender's hostname
    %(SENTBY_HELO)s     - sender's HELO/EHLO string
    %(DATETIME)s        - date and time in standard format ("%c")
    %(SYSLOG_DATE)s     - date and time in syslog format ("%a %e %H:%M:%S")
    %(PID)s             - current process ID
  
  You also can use log.FORMAT for default format or log.SUMMARY_REPORT
  for summary reporter script.
  
  Usage: log(logto,format,scanners...)
  
  Where: logto is a string, which defines filename to store these data
           If logto is an integer, it defines log level in standard
           log file.
         format is a string, which defines data format
  
  New format style is introduced in version 0.9.0, for older versions please
  use old format (for example "$STATUS" instead of "%(STATUS)s").