append time to ldap cache key

PcfAnnuaire.py

@@ -52,7 +52,10 @@ class PcfAnnuaireService:
     pass
 
 def cache_key(method, self):
-    return hash(self)
+    # append time, so old entries do not get returned forever; (they will still
+    # get removed as stale entries are automatically removed after 3 days)
+    # (cf plone/memoize/volatile.py)
+    return hash(self) + repr(int(time.time()) / 300)
 
 class PcfAnnuaire(BaseContent):