Only refresh when waitfor is an attribute.

Silly workaround for the fact that tests set the answers, but not the inputs,
  so refreshAnswers changes the test result even though it shouldn't.

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

@@ -136,7 +136,7 @@ class @Problem
   # invalid. To do so, the callee must throw an exception named "Waitfor
   # Exception". This and any other errors or exceptions that arise from the
   # callee are rethrown and abort the submission.
-  # 
+  #
   # In order to use this feature, add a 'data-waitfor' attribute to the input,
   # and specify the function to be called by the check button before sending
   # off @answers
@@ -145,13 +145,13 @@ class @Problem
       if ($(inp).is("input[waitfor]"))
         try
           $(inp).data("waitfor")()
+          @refreshAnswers()
         catch e
           if e.name == "Waitfor Exception"
             alert e.message
           else
             alert "Could not grade your answer. The submission was aborted."
           throw e
-    @refreshAnswers()
 
 
   ###
@@ -164,7 +164,6 @@ class @Problem
   check_fd: =>
     Logger.log 'problem_check', @answers
 
-
     # If there are no file inputs in the problem, we can fall back on @check
     if $('input:file').length == 0
       @check()