/*
 *  call-seq:
 *     dvector.reverse_each3(other1, other2) {|x,y,z| block } 
 *  
 *  Same as <code>Dvector#each3</code>, but traverses vectors in reverse
 *  order.  The vectors must have the same size.
 *     
 *     a = Dvector[ 1, 0, -1 ]
 *     b = Dvector[ 3, 4, 5 ]
 *     c = Dvector[ 6, 9, 2 ]
 *     a.reverse_each3(b, c) {|x,y,z| print "(", x ",", y, ", ", z, ") " }
 *     
 *  produces:
 *     
 *      (-1,5,2) (0,4,9) (1,3,6)
 */ VALUE dvector_reverse_each3(VALUE ary, VALUE ary2, VALUE ary3) {