/*
 * Free an Imlib2::Image object, and (optionally) de-cache it as well.
 *
 * Note: Any future operations on this image will raise an exception.
 *
 * Examples:
 *   # free image
 *   im.delete! 
 *
 *   # free image, and de-cache it too
 *   im.delete!(true)
 * 
 */
static VALUE image_delete(int argc, VALUE *argv, VALUE self) {