[Paraview] Animation with sudden large intervals between consecutive frames

[Utkarsh Ayachit]

> I'd like to find out why the offscreen is so much slower - does the offscreen redering session get created and destroyed on every frame. When generating 2000frames or so it can make a big difference.

I just verified that it doesn't do that i.e. doesn't create and
destroy the context on every frame when saving out animations.

Utkarsh