Ship (and optionally use) ext.h from clinfo to replace CL/cl_ext.h

Build error fix for when CL_USE_SHIPPED_EXT=False and CL/cl_ext.h doesn't define cl_device_topology_amd struct.

Added CL_USE_SHIPPED_EXT Switch in setup.py to use src/c_wrapper/clinfo_ext.h instead of CL/cl_ext.h.

Add clinfo_ext.h file taken from https://github.com/Oblomov/clinfo/blob/master/src/ext.h  version 271b88488df434eb68eb2d05996c39b5d78fe50b.

Fixes  for _enqueue_*_buffer_rect

Fixes for pyopencl.cffi_cl._enqueue_read_buffer_rect and pyopencl.cffi_cl._enqueue_write_buffer_rect, minor change to pyopencl.cffi_cl._enqueue_copy_buffer_rect to tuple-ise the pitch arguments.

Unit tests (test/test_enqueue_copy.py) for _enqueue_read_buffer_rect, _enqueue_write_buffer_rect and _enqueue_copy_buffer_rect.