Cycles:

* Add alpha pass output, to use set Transparent option in Film panel.
* Add Holdout closure (OSL terminology), this is like the Sky option in the
  internal renderer, objects with this closure show the background / zero
  alpha.
* Add option to use Gaussian instead of Box pixel filter in the UI.
* Remove camera response curves for now, they don't really belong here in
  the pipeline, should be moved to compositor.

* Output full float values for rendering now, previously was only byte precision.
* Add a patch from Thomas to get a preview passes option, but still disabled
  because it isn't quite working right yet.
* CUDA: don't compile shader graph evaluation inline.
* Convert tabs to spaces in python files.

intern/cycles/kernel/kernel_shader.h

@@ -342,6 +342,26 @@ __device void shader_emissive_sample(KernelGlobals *kg, ShaderData *sd,
 	}
 }
 
+/* Holdout */
+
+__device float3 shader_holdout_eval(KernelGlobals *kg, ShaderData *sd)
+{
+#ifdef WITH_OSL
+	if(kg->osl.use) {
+		return OSLShader::holdout_eval(sd);
+	}
+	else
+#endif
+	{
+#ifdef __SVM__
+		if(sd->svm_closure == CLOSURE_HOLDOUT_ID)
+			return make_float3(1.0f, 1.0f, 1.0f);
+		else
+			return make_float3(0.0f, 0.0f, 0.0f);
+#endif
+	}
+}
+
 /* Surface Evaluation */
 
 __device void shader_eval_surface(KernelGlobals *kg, ShaderData *sd,