Ideally we wouldn't have exposed cogl-texture-pixmap-x11.h as a
top level header and would have just automatically included it in cogl.h
but we already have code that assumes it can be directly included.
This ensures we define __COGL_H_INSIDE__ as a reminder that it is a top
level header in case we later need to include other cogl internal cogl
headers which would cause a build time error without this defined.
Reviewed-by: Neil Roberts <neil@linux.intel.com>
