/*
 *  call-seq:
 *     dvector.abs   ->  a_dvector
 *  
 *  Returns of copy of _dvector_ with all entries replaced by their absolute values.
 *     
 *     a = Dvector[ 1, -2, -3, 4 ]
 *     a.abs   -> Dvector[ 1, 2, 3, 4 ]
 */ 
VALUE dvector_abs(VALUE ary) {