message: fix carbon copy impersonation vulnerability
  (CVE-2017-5589+)
diff: @@ -788,6 +788,7 @@ jsxc.xmpp = {
  onChatMessage: function(stanza) {
  var forwarded = $(stanza).find('forwarded[xmlns="' + jsxc.CONST.NS.FORWARD + '"]');
  var message, carbon;
  + var originalSender = $(stanza).attr('from');
  if (forwarded.length > 0) {
  message = forwarded.find('> message');
  @@ -796,6 +797,9 @@ jsxc.xmpp = {
  if (carbon.length === 0) {
  carbon = false;
  + } else if (originalSender !== Strophe.getBareJidFromJid(jsxc.xmpp.conn.jid)) {
  + // ignore this carbon copy
  + return true;
  }
  jsxc.debug('Incoming forwarded message', message);
  