Restore from XML fails if System Information contains dashes

The backup file contains the System Information as an XML comment at the beginning of the file. Certain character sequences are not valid in XML comments, like '--'.

Services allow the user to specify parameters as free text, and that information is reflected in the System Info page. That should be properly escaped, as not to allow the invalid XML sequences.

For instance, the following Service information will make the XML non-parseable, and the backup restore will fail:

handler.params: splitregex=/-----\s*Original Message\s*-----/,/______*/,catchemail=...