/*
 *  call-seq:
 *     dvector.pop -> number or nil
 *  
 *  Removes the last element from _dvector_ and returns it, or
 *  <code>nil</code> if the vector is empty.
 *     
 *     a = Dvector[ 1, 2, 3 ]
 *     a.pop   -> 3
 *     a       -> Dvector[ 1, 2 ]
 */ VALUE dvector_pop(VALUE ary) {