Created entity should populate created & changed by default.

Currently when creating an entity, the created & changed fields are empty.

This needs to be specified explicitly as below:

      $entity = entity_create('bundle',
          array(
            'type' => 'my_bundle',
            'created' => REQUEST_TIME,
            'changed' => REQUEST_TIME,
          ));
      $wrapper = entity_metadata_wrapper('my_bundle', $entity);
      $wrapper->save();