Add compatibility with mods that uses the second argument in add_integration

fixes #2382

And this is why I prefer this:

``` php
add_integration_function('integrate_menu_buttons', '$sourcedir/SomeFile.php|Class::method#');
```

over this:

``` php
add_integration_function('integrate_menu_buttons', 'Class::method', true, '$sourcedir/SomeFile.php', true);
```

Signed-off-by: Suki <suki@missallsunday.com>