/*
 *  call-seq:
 *     dvector.resize(new_size)  -> dvector
 *
 *  Modifies _dvector_ to have the requested size by truncating or expanding with trailing zeros.
 *
 *  a = Dvector[1, 5, -3]
 *  a.resize(5)            -> Dvector[ 1, 5, -3, 0, 0 ]  
 *  a                      -> Dvector[ 1, 5, -3, 0, 0 ]  
 *  a.resize(2)            -> Dvector[ 1, 5 ]  
 *  a                      -> Dvector[ 1, 5 ]  
 */ 
VALUE dvector_resize(VALUE ary, VALUE len) {