/*
 *  call-seq:
 *     dvector.abs!   ->  dvector
 *  
 *  Replace each entry x of _dvector_ with abs(x).
 *     
 *     a = Dvector[ 1.1, -2.2, 5.3 ]
 *     a.abs!   -> Dvector[ 1.1, 2.2, 5.3 ]
 *     a        -> Dvector[ 1.1, 2.2, 5.3 ]
 */ 
VALUE dvector_abs_bang(VALUE ary) {