/*
 * call-seq:
 *  easy.on_missing {|easy,code| ... }                => <old handler;>
 *
 *  Assign or remove the on_missing handler for this Curl::Easy instance.
 *  To remove a previously-supplied handler, call this method with no attached
 *  block.
 *
 *  The +on_missing+ handler is called when request is finished with a 
 *  status of 40x
 */
static VALUE ruby_curl_easy_on_missing_set(int argc, VALUE *argv, VALUE self) {