/*
 *  call-seq:
 *     dvector.round   ->  a_dvector
 *  
 *  Returns of copy of _dvector_ with each entry x replaced by round(x).
 *  (Numbers midway between integers round away from zero.)
 *     
 *     a = Dvector[ 1.1, -2.2, 5.3 ]
 *     a.round   -> Dvector[ 1, -2, 5 ]
 */ 
VALUE dvector_round(VALUE ary) {