CCEffectNode - Add initializers with the same parameters as CCRenderTexture

And add convenience constructors too.
CCEffectsTest - Add a test of clipping combined with effects

A clipping node renders into an effect node with an attached pixellate effect.
CCEffectNode - Fix CCClippingNodes as children of CCEffectNode

Even if it had a stencil buffer, CCEffectNode was only clearing the color buffer.