/*
* 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) {