* fix buggy prototype usage in Pass derived classes.

* remove constructors as suggested by @mrdoob

* fix MaskPass's prototype.

* 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.

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).

Not sure yet about names and location of files.