attach an unencrypted explanatory body to XEP-0200 encrypted messages

src/common/stanza_session.py

@@ -249,6 +249,9 @@ def encrypt_stanza(self, stanza):
 		c.NT.mac = base64.b64encode(self.hmac(self.km_s, m_content + \
 			crypto.encode_mpi(old_en_counter)))
 
+		stanza.setBody(_('[This message is part of an encrypted session. '
+		'If you see this message, something went wrong.]'))
+
 		return stanza
 
 	def is_xep_200_encrypted(self, msg):
@@ -950,4 +953,4 @@ def cancelled_negotiation(self):
 
 		self.km_o = ''
 
-# vim: se ts=3:
\ No newline at end of file
+# vim: se ts=3: