marked "urgent" are considered to be higher priority than other messages
and so they will be played before any other messages in a user's mailbox.

There are two ways to leave an urgent message. 
1. send the 'U' option to VoiceMail().
2. Set review=yes in voicemail.conf. This will give instructions for 
   a caller to mark a message as urgent after the message has been recorded.

I have tested that this works correctly with file and ODBC storage, and James
Rothenberger (who wrote initial support for this feature) has tested its use
with IMAP storage.

(closes issue #11817)
Reported by: jaroth
	Based on branch http://svn.digium.com/svn/asterisk/team/jrothenberger/asterisk-urgent
Tested by: putnopvut, jaroth



git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@115588 65c4cc65-6c06-0410-ace0-fbb531ad65f3