edev: Guest User messaging fix

There is a small bug where a user can message Guest_User; the messages could pile up there (and now that they can't see other users or the catbox), this may be trouble. They can see how many messages guest user has, but message inbox is locked out for the guest user.

A simple fix would be to add a feedback message if they tried to message Guest_User (for whatever reason). At about line 49 in the message opcode (node 445058), you could add the following code:

if(getID($U) == $HTML_VARS{guest_user}) {
	$DB->sqlInsert('message', {msgtext => "Screaming at the darkness?  $user can't hear you.  Try the chatterbox; someone may love you there.", author_user => getId(getNode('root','user')), for_user =>getId($USER) });
  	return;
}

Note, I haven't tested the code, but I adapted it from the code that was already there. Editors / godtypes, please wipe out my two messages from Guest_User that I used to try and test the bug. Comments welcome.

My perl is weak, and it's my first submission. Please be gentle.