Fix clamdscan configuration handling
Fix clamdscan configuration handling

 - Honor configured 'false' values
 - Treat 'scan_all' consistently with other options--permitting 0, 1, 'yes', or 'no' as values

msimerson/qpsmtpd,msimerson/qpsmtpd,sieutruc/qpsmtpd,salvis/qpsmtpd,priyadi/qpsmtpd,priyadi/qpsmtpd,sieutruc/qpsmtpd,sieutruc/qpsmtpd,salvis/qpsmtpd,smtpd/qpsmtpd,priyadi/qpsmtpd,smtpd/qpsmtpd