MailSettings doesn't handle markup in content element

[phtyson]

The org.yawlfoundation.yawl.util.MailSettings.toXML() method (and probably fromXML() as well) fails when the content parameter contains markup.

I don't know enough jdom, or the yawl XNode utility, to suggest a fix.

As far as I can tell, the toXML() method is not called in normal operations. I was using it to debug mailservice calls, and after getting mysterious unlogged failures, I eventually found the toXML() method was failing silently.