PostProcessing: Add support for user-supplied anaglyph shaders.

There are lots of different anaglyph glasses out there and there may be even more creative uses for stereoscopic post-processing shaders.

Data/Sys/Shaders/Anaglyph/grayscale2.glsl

@@ -0,0 +1,12 @@
+// Anaglyph Red-Cyan luma grayscale shader
+// Info: http://www.oreillynet.com/cs/user/view/cs_msg/8691
+
+void main()
+{
+	float3 luma = float3(0.222, 0.707, 0.071);
+	float4 c0 = SampleLayer(0);
+	float avg0 = dot(c0.rgb, luma);
+	float4 c1 = SampleLayer(1);
+	float avg1 = dot(c1.rgb, luma);
+	SetOutput(float4(avg0, avg1, avg1, c0.a));
+}