in_response_to metadata added.

svn path=/plone.app.discussion/trunk/; revision=27789

plone/app/discussion/catalog.py

@@ -60,6 +60,10 @@ def description(object):
 def searchable_text(object):
     return object.title, object.text
 
+@indexer(IComment)
+def in_response_to(object):
+    return object.__parent__.__parent__.title_or_id()
+
 @indexer(IComment)
 def effective(object):
     # the catalog index needs Zope DateTime instead of Python datetime