#1228. Added more descriptive error message, when trying to insert ne…

…w column to a table with object datasource.

src/core.js

@@ -202,7 +202,9 @@ Handsontable.Core = function (rootElement, userSettings) {
      */
     createCol: function (index, amount) {
       if (priv.dataType === 'object' || priv.settings.columns) {
-        throw new Error("Cannot create new column. When data source in an object, you can only have as much columns as defined in first data row, data schema or in the 'columns' setting");
+        throw new Error("Cannot create new column. When data source in an object, " +
+          "you can only have as much columns as defined in first data row, data schema or in the 'columns' setting." +
+          "If you want to be able to add new columns, you have to use array datasource.");
       }
       var rlen = instance.countRows()
         , data = GridSettings.prototype.data