mod_mam: Specify namespace for MAM messages

The "jabber:client" namespace must be explicitly specified for MAM
messages, as they would otherwise inherit the "urn:xmpp:forward:0"
namespace.

mod_mam/src/mod_mam.erl

@@ -867,7 +867,9 @@ send_mam_message(#jid{luser = U, lserver = S} = JID, QueryID,
 		    attrs = [{<<"xmlns">>, ?NS_HINTS}]},
     Forwarded = #xmlel{name = <<"forwarded">>,
 		       attrs = [{<<"xmlns">>, ?NS_FORWARD}],
-		       children = [Stanza]},
+		       children = [xml:replace_tag_attr(<<"xmlns">>,
+							<<"jabber:client">>,
+							Stanza)]},
     Result = #xmlel{name = <<"result">>,
 		    attrs = [{<<"xmlns">>, ?NS_MAM},
 			     {<<"id">>, jlib:integer_to_binary(MamID)}]