Simplified the code involving if( variable === undefined ) and fixed `String.prototype.trim` bug.

Correction in ColorUtils-a new color object is not returned, but the original object is modified in place instead.

Using the full THREE.LineStrip and THREE.LinePieces constants in the docs as it makes it more explicit and avoids guessing (is it a String? is it a constant?)

Is not exactly the same beaviour. object.traverse also applied the callback to object.
But I think it's better like this, because now we can do object.traverse( function ( node ) { node.visible = false } ) and it will also take care of the parent. However, if this creates any problem we can revert the behaviour.
I also prefer this behaviour because the code is simpler/cleaner :P

See discussion #2412

Renamed screen shader to blit.
Throwing errors in *Pass if the shader aren't available.

The following examples where broken on mrdoob.github.com and when
viewed through a local python web server. file:// worked.

webgl_loader_collada.html
webgl_loader_collada_keyframe.html
webgl_loader_json_blender.html

@alteredq: I think ShaderExtras.js is starting to become bulky and messy... What do you think about splitting ShaderExtras into single files? Contributing new shaders would then feel more welcoming. And the examples would show the dependencies clearer.

I was unsure on what style use... THREE.WebGLShaders['film'], THREE.FilmWebGLShader or THREE.FilmShader. The later seemed the nicest

For the moment tried to keep it as dumb as possible: one string for define label, another string for define value.

I'm not yet fully sure of all the details but that's something I wanted to do for a long time, to be able to have user-configurable way for baked-in parameters (for use cases like the convolution filter).

See #2412

Fixes #2419

- attempts to fix issue mentioned in #2417
- a bit of refactoring, more should come
- the sharp edges, ceases thing should be revisited

Finally it was much simpler issue than I thought ;)