Native bindings to the EXT_occlusion_query_boolean extension.

This extension defines a mechanism whereby an application can query whether any pixels (or, more precisely, samples) are drawn by a primitive or group of primitives.

The primary purpose of such a query (hereafter referred to as an "occlusion query") is to determine the visibility of an object. Typically, the application will render the major occluders in the scene, then perform an occlusion query for each detail object in the scene. On subsequent frames, the previous results of the occlusion queries can be used to decide whether to draw an object or not.