Implemented GL_ARB_occlusion_query (not 100% finalized).
diff --git a/docs/RELNOTES-5.1 b/docs/RELNOTES-5.1
index 0a38006..d061991 100644
--- a/docs/RELNOTES-5.1
+++ b/docs/RELNOTES-5.1
@@ -60,6 +60,9 @@
 GL_EXT_texture_rectangle
    Identical to GL_NV_texture_rectangle
 
+GL_ARB_occlusion_query
+   Useful for visibility-based culling.
+
 
 
 Build System Changes