Report Jython errors to user - addresses #694

- may need to work on the format a bit more

extensions/jython/src/com/google/refine/jython/JythonEvaluable.java

@@ -128,7 +128,7 @@ public class JythonEvaluable implements Evaluable {
 
             return unwrap(result);
         } catch (PyException e) {
-            return new EvalError(e.getMessage());
+            return new EvalError(e.toString());
         }
     }