Allow error-template-rendering errors to propagate to top-level 500 handler

* hopefully won't come up, but if they do, our 500 page
  should be better than  HttpResponse("There was an unrecoverable error")

lms/djangoapps/courseware/views.py

@@ -187,7 +187,10 @@ def index(request, course_id, chapter=None, section=None,
                                             {'staff_access': staff_access,
                                             'course' : course})
             except:
-                result = HttpResponse("There was an unrecoverable error")
+                # Let the exception propagate, relying on global config to at
+                # at least return a nice error message
+                log.exception("Error while rendering courseware-error page")
+                raise
 
     return result