Replace dynamite code with tested version

lms/static/coffee/src/modules/problem.coffee

@@ -15,6 +15,7 @@ class @Problem
     @$('section.action input.reset').click @reset
     @$('section.action input.show').click @show
     @$('section.action input.save').click @save
+    @$('input.math').keyup(@refreshMath).each(@refreshMath)
 
   render: (content) ->
     if content
@@ -62,6 +63,20 @@ class @Problem
       if response.success
         alert 'Saved'
 
+  refreshMath: (event, element) =>
+    element = event.target unless element
+    target = "display_#{element.id.replace(/^input_/, '')}"
+
+    if jax = MathJax.Hub.getAllJax(target)[0]
+      MathJax.Hub.Queue ['Text', jax, $(element).val()]
+
+      try
+        output = jax.root.toMathML ''
+        $("##{element.id}_dynamath").val(output)
+      catch exception
+        throw exception unless exception.restart
+        MathJax.Callback.After [@refreshMath, jax], exception.restart
+
   refreshAnswers: =>
     @$('input.schematic').each (index, element) ->
       element.schematic.update_value()