Fix total_comments indexer

"@property removes Acquisition wrappers from 'self'.
I don't remember why exactly (some implementation detail of Acquisition),
but it's a fact of life."

Quote from @davisagli on
https://github.com/plone/plone.app.discussion/pull/58

In short: removing the @property from total_comments fix the problem.

plone/app/discussion/catalog.py

@@ -33,7 +33,7 @@ def total_comments(object):
     if object.meta_type != 'Discussion Item':
         try:
             conversation = IConversation(object)
-            return conversation.total_comments
+            return conversation.total_comments()
         except TypeError:  # pragma: no cover
             # The item is contentish but nobody
             # implemented an adapter for it

plone/app/discussion/conversation.py

@@ -77,7 +77,6 @@ class Conversation(Traversable, Persistent, Explicit):
         parent = aq_inner(self.__parent__)
         return parent.restrictedTraverse('@@conversation_view').enabled()
 
-    @property
     def total_comments(self):
         public_comments = [
             x for x in self.values()