They were immediately deleted when the associated thinker was destroyed. But this was too early because it missed the final tic of movement, resulting in a visible jump when a moving platform with a player on it came to a halt.
Changed it so that DelRef no longer destroys the interpolation itself. Instead the ::Interpolate method will check if the reference count is 0, and if so and there was no more movement, will then destroy the interpolation.
This ensures that it keeps running until it has interpolated all remaining bits of movement induced by the thinker.
Now moving up a lift is 100% smooth, even with movement interpolation on.
* FInterpolator depended on external references to prevent its content from getting GC'd.
* none of the pointers in the interpolation objects were declared to the GC.
The result of these issues was that changing anything about the life cycle of interpolation objects caused corrupted memory crashes when a level was changed.
