/*
 *  call-seq:
 *     dvector.asin!   ->  dvector
 *  
 *  Replace each entry x of _dvector_ with asin(x).
 *     
 *     a = Dvector[ 0.1, -0.2, 0.3 ]
 *     a.asin!   -> Dvector[ asin(0.1), asin(-0.2), asin(0.3) ]
 *     a         -> Dvector[ asin(0.1), asin(-0.2), asin(0.3) ]
 */ 
VALUE dvector_asin_bang(VALUE ary) {