Distorted Android

1. Make it possible to enable/disable DEPTH test when rendering to a Screen
2. Using this, remove the 'Root' Node from StarWars.

A lot of different fixes.

A lot of issues still there:

1) if we only render part of the tree, tree isomorphism will sometimes not work correctly
2) when we change Effects that are inside Trees mid-render, even if we detach() the affected parts of the Tree first, for the last frame the new Effects will be used...

New, cleaner way to create/destroy DistortedSurfaces.

Serious regression in StarWars (crashes!). Looks like the Node's internal FBO is being deleted and not re-created in time.

Minor.

Fix the Effects3D regression.

Some progress with fixing the efects3D regression. Not done yet.

Change the the render() API!

THis introduces some regressions with the Effects3D app.

Preparation for change of the render API.

Minor

Major: change of API.

Split DFramebuffer into Framebuffer and Screen; introduce the 'DistortedInputSurface' and 'DistortedOutputSurface' interfaces.