The deprecation of "username" in favor of "defaultuser" for SIP peers unfortunately

broke realtime configurations which still used the "username" field. This was taken
care of properly when reading from realtime but was not handled properly when updating
a realtime peer. This change also adds a deprecation NOTICE CLI message that will print
if using the deprecated "username" field.

(closes issue #11880)
Reported by: cabal95
Patches:
      11880.patch uploaded by putnopvut (license 60)
	  Tested by: cabal95



git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@101344 65c4cc65-6c06-0410-ace0-fbb531ad65f3