Switch to side-by-side view

--- a/Allura/allura/model/discuss.py
+++ b/Allura/allura/model/discuss.py
@@ -379,7 +379,7 @@
             return None
 
     def reply_subject(self):
-        if self.subject.lower().startswith('re:'):
+        if self.subject and self.subject.lower().startswith('re:'):
             return self.subject
         else:
             return 'Re: ' +(self.subject or '(no subject)')