/*
 *  call-seq:
 *     dvector.min   ->  number or nil
 *     dvector.min(dvector2, ...)   ->  number or nil
 *  
 *  First form returns the entry with the minimum value in _dvector_, <code>nil</code> if
 *  _dvector_ is empty.  Second form returns minimum of all the vectors (or <code>nil</code> if all are empty).
 *     
 *     a = Dvector[ 1, 2, 3, 4, 5, 4, 3, 5, 2 ]
 *     a.min               -> 1
 *     Dvector[].min          -> nil
 *     b = Dvector[ 8, 3, 0, 7 ]
 *     a.min(b)            -> 0
 */ 
VALUE dvector_min(int argc, VALUE *argv, VALUE self) {