The email_start_finalbody hook is missing...

I wrote my own extension so that members of my site would receive only 3 emails before the “accept_admin_email” setting on their account would be set to N. This extension also tacks on a message about the feature to every outgoing email, but it requires the email_start_finalbody hook, which doesn’t exist in EE 2.1.3.

I added it, and would appreciate any insight from EE developers on any issues my alteration of the code might cause. I added the following two lines at the top of the _build_message function in /codeigniter/system/libraries/Email.php:

$this->Ext = new EE_Extensions();
$this->Ext->call('email_start_finalbody',$this);