Added function shmop_sys_shmid(shmop_resource). Returns the underlying system shmid from the shmop resource identifier returned by shmop_open().

Example usage:
    if($shm_id = shmop_open(0xdeadbeef, 'c', 0666, 1024)) {
       $sys_shmid = shmop_sys_shmid($shm_id);
       echo `ipcs |grep $sys_shmid`;
    }

Output:
    0xdeadbeef 1719894051 nedwidek   666        1024       1