/*
 * Set the size (in bytes) of the application-wide image cache.
 *
 * Examples:
 *   new_size = 16 * 1024 ** 2               # 16 megabytes
 *   Imlib2::Cache::set_image_cache new_size
 *
 *   new_size = 16 * 1024 ** 2               # 16 megabytes
 *   Imlib2::Cache::image_cache = new_size
 *
 *   new_size = 16 * 1024 ** 2               # 16 megabytes
 *   Imlib2::Cache::image = new_size
 */
static VALUE cache_set_image(VALUE klass, VALUE val) {