* fix buggy prototype usage in Pass derived classes.

* remove constructors as suggested by @mrdoob

* fix MaskPass's prototype.

* Examples: use .texture of input render targets.

* Assign null instead of undefined.

* Post-Processing: Introducing base class for Passes

* Post-Processing: move pass to effect composer

This reverts commit 644d6a21.

Conflicts:
	src/materials/Material.js

This commit enables three.js to manage the stencil buffer via material
properties.

Otherwise we can't use defines in post processing shaders

This fixes # 2951.

All examples should work now.

The only weird thing seems to be that for some reason bone texture doesn't like to be assigned to arbitrary texture unit (or more precisely to alternating texture units).

See #2340

Do not use for anything, this is just snapshot of a test in progress. I solved quite a few issues, but many things are still clumsy and broken.

Added ability to disable render passes to EffectComposer. Added simple blend shader to ShaderExtras.

Added renderer.getClearAlpha. Extended RenderPass to be able to use custom alpha clear. Fixed UVs in UTF8Loader.

Cause everywhere there are warnings about not writing to the same texture which is also being read. Curiously enough this didn't make problems so far (save for mysterious lines when doing "heat" effect in ro.me).

Added generic ShaderPass. Removed SepiaPass, ScreenPass, VignettePass. Added bleachbypass shader. Simplified multi-composer pipeline in postprocessing example.

Not sure yet about names and location of files.