Small changes to improve the core

My proposed changes:

1) Few lines in module_m.php that I thought could be improved for performance.

2) A plain distraction bug on MY_Controller.php.

3) On streams_core/libraries/Fields.php I made a very small change to make stream inserts friendly for ajax requests by being able to avoid insertion of messages to flashvars by giving them FALSE.
Also streams_core/libraries/Fields.php:230, had a wrong variable in use regardless of my changes:

$this->CI->session->set_flashdata('notice', $this->CI->fields->translate_label($failure_message));

Should be

$this->CI->session->set_flashdata('notice', $this->CI->fields->translate_label($extra['failure_message']));

Regards.