Warning in PostProcessLayer InspectorGUI for SPS and pre-2017.2

SPS is only officially supported in 2017.2+ because of XRSettings.eyeTextureDesc.  There are manual workarounds, but they aren't configured yet.  Might be in the future.

Author: robbiesri

PostProcessing/Editor/PostProcessLayerEditor.cs

@@ -116,6 +116,11 @@ public override void OnInspectorGUI()
 
             var camera = m_Target.GetComponent<Camera>();
 
+            #if !UNITY_2017_2_OR_NEWER
+            if (RuntimeUtilities.isSinglePassStereoEnabled)
+                EditorGUILayout.HelpBox("Unity 2017.2+ required for full Single-pass stereo rendering support.", MessageType.Warning);
+            #endif
+
             DoVolumeBlending();
             DoAntialiasing();
             DoFog(camera);