* Throw an error if template signal uses the 'object' attribute since we don't support GObject.signal_connect_object()
* Throw an error if template signal sets the 'swapped' attribute to 'true' since we don't support GObject.signal_connect_swapped() or @user_data
* Respect the flag for GObject.signal_connect_after()

* Throw an error if template signal uses the 'object' attribute
* Amend error messages to make it clearer they are template errors
* call set_connect_func() on the constructor object