Monitoring plugin does not add namespace
After OF-1087, (applied in 1.5.1) the Monitoring plugin stopped returning namespaces in messages that it returns as part of a retrieve-archive request.
As you can see in the reproduction below, the archived messages are returned without a namespace (look at the stanza with ID purpleed855cd3 for example).
If no 'xmlns' is set for the stanza then as per XML namespacing rules it would inherit the 'urn:xmpp:forward:0' namespace, which is wrong (see XEP-0297).
Stanzas should be saved with their original namespace (which will cause them to be returned with their original namespace), but as that won't fix existing archives, and the only stanza being saved is a message stanza, the namespace perhaps could be reconstructed when constucting the MAM response.