Merging HalftoneShader and ConvolutionShader hardfails

[boytchev]

ConvolutionShader after HalftoneShader causes compilation fail in shaders:

• vertex shader: 'KERNEL_SIZE_FLOAT' : undeclared identifier
• fragment shader: 'KERNEL_SIZE_INT' : undeclared identifier

var effects = new Effects( renderer )
		.addEffect( HalftoneShader )
		.addEffect( ConvolutionShader )