const()
  Realscanner to return a constant value (virus or clean).
  
  This scanner has no special functionality. It returns always
  a defined virus, or clean (if virus is not defined).
  This scanner has no error codes.
  
  Usage: const(level, VirName, return_string=[])
      or const()
  
  Where: level is an float which defines returned infection level
           If level is not defined, after scanning an error is raised.
         VirName is a returned virus.
         return_string is a array of strings returned
  
  Examples: const(0.0)          # Return clean
            const(1.0, 'Virus') # Return virus name "Virus"
            const()             # Raise an error