Fixed bug when user votes w/o permission - now displays a friendly error message instead of failing.

Fixed bug when hinter module displays a hint, then is asked to display nothing.  (Used to not update in this case.)

common/lib/xmodule/xmodule/crowdsource_hinter.py

@@ -227,7 +227,7 @@ class CrowdsourceHinterModule(CrowdsourceHinterFields, XModule):
         Returns key 'hint_and_votes', a list of (hint_text, #votes) pairs.
         """
         if self.user_voted:
-            return json.dumps({'contents': 'Sorry, but you have already voted!'})
+            return {}
         ans_no = int(get['answer'])
         hint_no = str(get['hint'])
         answer = self.previous_answers[ans_no][0]

common/lib/xmodule/xmodule/js/src/crowdsource_hinter/display.coffee

@@ -72,3 +72,5 @@ class @Hinter
       JavascriptLoader.executeModuleScripts @el, () =>
         @bind()
       @$('#previous-answer-0').css('display', 'inline')
+    else
+      @el.hide()