/*
 *  call-seq:
 *     dvector.each2(other) {|x,y| block } 
 *  
 *  Calls <i>block</i> once for each element in _dvector_, passing that
 *  element as a parameter along with the corresponding element from the _other_ vector.
 *  The two vectors must be the same length.
 *     
 *     a = Dvector[ 1, 0, -1 ]
 *     b = Dvector[ 3, 4, 5 ]
 *     a.each2(b) {|x,y| print "(", x ",", y, ") " }
 *     
 *  produces:
 *     
 *     (1,3) (0,4) (-1,5) 
 */ VALUE dvector_each2(VALUE ary, VALUE ary2) {