dialog_add_js() : function does not exist

Ditto here. I was receiving a fatal error, and commenting it out was the fix.
The function is also removed in the patch attached to #1246328: Schedule a campaign (Send it on a specific datetime), with the same comment.

Probably a better way of dealing with the problem was enabling Dialog API module , which has this function defined.

Since the dialog module is not in the dependency list, I wrapped it in a if statement, so we can still have it running if the module/function exists.

<?php
if (module_exists('dialog') && function_exists('dialog_add_js')) {
  dialog_add_js();
}
?>

Already committed to the latest dev.