core (disco), plugin XEP-0115: client use + capabilities hash improvment:

- modified a couple of method from memory to use client instead of profile
- XEP-0115: don't use unique hash for all clients anymore, as disco can be different between clients/components, and even between clients (different identity for instance).
    hash is now generated per client on each new session.

src/memory/disco.py

@@ -284,6 +284,9 @@ class Discovery(object):
         found_entities = set()
 
         def infosCb(infos, entity):
+            if entity is None:
+                log.warning(_(u'received an item without jid'))
+                return
             if identity is not None and identity not in infos.identities:
                 return
             if features.issubset(infos.features):