libs/gst/controller/: Add a new private GstControlPoint struct which "inherits" from

libs/gst/controller/: Add a new private GstControlPoint struct which "inherits" from

Original commit message from CVS:
reviewed by: Stefan Kost <ensonic@users.sf.net>
* libs/gst/controller/gstcontroller.c: (gst_control_point_compare),
(gst_control_point_find), (gst_controlled_property_new),
(gst_control_point_free), (gst_controlled_property_free),
(gst_controller_set), (gst_controller_set_from_list),
(gst_controller_unset), (gst_controller_unset_all),
(gst_controller_sync_values):
* libs/gst/controller/gstcontroller.h:
* libs/gst/controller/gstcontrollerprivate.h:
* libs/gst/controller/gstinterpolation.c:
(gst_controlled_property_find_control_point_node),
(interpolate_none_get), (interpolate_trigger_get):
Add a new private GstControlPoint struct which "inherits" from
GstTimedValue to allow different interpolators to store internal
values next to each control point. From the outside everything is
still a GstControlPoint so we don't loose binary compatibility.
Also fixup all the GValue handling to not leak GValues or list nodes.
* tests/check/libs/controller.c: (GST_START_TEST):
Free the list nodes and GValues in the controller_misc test.