check_level()
  Select scanner based on tested scanner return status.
  
  Usage: check_level(tested_scanner, {
                       (min,max): scanner,
                       (min,max): scanner, ...
                     })
     or: check_level()
  
  Where: tested_scanner is a scanner, which return level will be tested
         min is an integer, minimal level for this scanner
         max is an integer, maximal level for this scanner
  
  This scanner with no arguments will return previously saved status.
  Evaluation function is: min <= LEVEL < max .
  When no range is found, cached reply will be returned without changes.
  
  Example: check_level(spamassassind(), {
               (1.0, 5.0):     deliver(
                                 modify_subject('[SPAM:%L]',
                                   check_level()
                                 )
                               ),
               (5.0, 99999.0): drop('.', check_level())
           })
  
  New in version 0.9.0.