Undocumented slot_base::track_container_type and slot_base::tracked_objects(),

as they are no longer worth documentation due to the changes required to support
tracking foreign shared_ptr types.


[SVN r65648]

libs/signals2

@@ -1 +1 @@
-Subproject commit 09c3f6cdbffcea10759ee6f033b92fb1f0cd5ce3
+Subproject commit 15bdfedced3951d826c3eaa5ffd19436f8eb41b3