/*
 *  call-seq:
 *     dvector.each2_with_index(other) {|x,y,index| block } 
 *  
 *  Calls <i>block</i> once for each element in _dvector_, passing the 
 *  element, the corresponding element from the _other_ vector, and the index.
 *     
 *     a = Dvector[ 1, 0, -1 ]
 *     b = Dvector[ 3, 4, 5 ]
 *     a.each2_with_index(b) {|x,y,i| print "(", x ",", y, ",", i, ") " }
 *     
 *  produces:
 *     
 *     (1,3,0) (0,4,1) (-1,5,2) 
 */ VALUE dvector_each2_with_index(VALUE ary, VALUE ary2) {