Native bindings to the khr_initialize_memory extension.

This extension adds support for initializing local and private memory before a kernel begins execution.

Memory is allocated in various forms in OpenCL both explicitly (global memory) or implicitly (local, private memory). This allocation so far does not provide a straightforward mechanism to initialize the memory on allocation. In other words what is lacking is the equivalent of calloc for the currently supported malloc like capability. This functionality is useful for a variety of reasons including ease of debugging, application controlled limiting of visibility to previous contents of memory and in some cases, optimization.