/*
 *  call-seq:
 *     dvector.join(sep=" ")    -> a_string
 *  
 *  Returns a string created by converting each element of the vector to
 *  a string, separated by <i>sep</i>.
 *     
 *     Dvector[ 1, 2, 3 ].join        -> "1 2 3"
 *     Dvector[ 1, 2, 3 ].join("-")   -> "1-2-3"
 */ 
VALUE dvector_join_m(int argc, VALUE *argv, VALUE ary) {