Keep thread sorting order stable when sorting by comments or votes by using

created_at time as a tiebreaker. This is a stopgap though; the service should handle
this. But it looks silly with things shuffling around right now.

lms/static/coffee/src/discussion/content.coffee

@@ -129,6 +129,12 @@ if Backbone?
       json_attributes = _.clone(@attributes)
       _.extend(json_attributes, { title: @display_title(), body: @display_body() })
 
+    created_at_date: ->
+      new Date(@get("created_at"))
+
+    created_at_time: ->
+      new Date(@get("created_at")).getTime()
+
   class @Comment extends @Content
     urlMappers:
       'reply': -> DiscussionUtil.urlFor('create_sub_comment', @id)

lms/static/coffee/src/discussion/discussion.coffee

@@ -66,9 +66,15 @@ if Backbone?
     sortByVotes: (thread1, thread2) ->
       thread1_count = parseInt(thread1.get("votes")['up_count'])
       thread2_count = parseInt(thread2.get("votes")['up_count'])
-      thread2_count - thread1_count
+      if thread2_count != thread1_count
+        thread2_count - thread1_count
+      else
+        thread2.created_at_time() - thread1.created_at_time()
 
     sortByComments: (thread1, thread2) ->
       thread1_count = parseInt(thread1.get("comments_count"))
       thread2_count = parseInt(thread2.get("comments_count"))
-      thread2_count - thread1_count
+      if thread2_count != thread1_count
+        thread2_count - thread1_count
+      else
+        thread2.created_at_time() - thread1.created_at_time()