Change default for QUARANTINE_USE_FLAG

nowadays no one uses MailScanner less than v4.43  anymore (I strongly hope!).
also changed username and password to make less tempting the use of root mysql user.
Updating install instruction for new QUARANTINE_USE_FLAG default
adding missing $mta initalization

fix #93
updated mysql CREATE query to be compatible with MySQL 5.0 or newer
upgrading xmlrpc lib