The last enabled EffectComposer pass is the only one that can really render to the screen, so we can set the renderToScreen flag in the passes automatically. The only case where EffectComposers don't render to the screen at all in the current examples is webgl_materials_skin, that sets up multiple EffectComposers and then combines their results. For that special case we now have a renderToScreen flag in EffectComposer.

This simplifies setting up EffectComposer and will make further enhancements a bit easier.

* start of background pass test.

* get clear pass and texture pass working well with each other.

* cube texture pass works.  render pass now obeys Pass.clear.  CubeTexturePass supports opacity.  TexturePass doesn't write to the depth buffer.

* get rid of temp matrix.

* add to files.js.  better title.

* remove unused scene parameter from CubeTexturePass.

* support custom clear colors in ManuallMSASRenderPass like RenderPass supports.

* fix bugs in clearColor/clearAlpha for MSAA.

* cleanup.

* simplify clearColor in ManualMSAARenderPAss + RenderPass.

* WestLAngley suggestion.

* use only one composer, rather than two.  Just turn on and off passes.  Allow for toggling autoRotate

* avoid allocating THREE.Color classes when possible.

* fixed.

* simplify code via automatic hoisting.

* hex rather than color.

* added .setViewOffset method to OrthographicCamera

* fixed .setViewOffset method

* added .clearViewOffset method

* added camera switcher to msaa_unbiased example

* renamed variables

* typo in docs

* added doc for perspective camera .clearViewOffset

* added doc for orthographic camera .set/.clearViewOffset

* add unbiased mode to the MSAA render pass.

* clearer code.

* better comment.

* cleanup code.  fix bug of using "camera", instead of "this.camera"

* fix more places were "camera" is used instad of "this.camera" -- it worked because example declared "camera" as a global.

* reduce light intensity.

* add PerspectiveCamera.clearViewOffset() per @mrdoob's recommendation.

* add Pass.setSize() and have it called automatically by EffectComposer.setSize()

* fix minor bugs in EffectComposer.setSize routine.

* fix buggy prototype usage in Pass derived classes.

* fix buggy prototype usage in Pass derived classes.

* remove constructors as suggested by @mrdoob

* fix MaskPass's prototype.

* init pass side when added to compositor.

* tabify EffectComposer.js

* simplify for loop.

rename MSAAPass -> ManualMSAARenderPass.  Remove 32 sample pattern (leads to rounding errors), simplify the shader.