1) collectpads2 has 0 direct tests
- the collectpads test should be reviewed and ported

2) collectpads2 still has stuff like gst_collect_pads2_is_active and gst_collect_pads2_collect which are unimplemented and are now part of the API again :/

3) does it make sense to keep gst_collect_pads2_add_pad and gst_collect_pads2_add_pad_full?

4) one still need the hack to override/extend the event function (e.g. in adder, avimux, ...)