/*
 *  call-seq:
 *     dtable.div(number)       ->  a_dtable
 *     dtable.div(other)        ->  a_dtable
 *     dtable - number          ->  a_dtable
 *     number - dtable          ->  a_dtable
 *     dtable - other           ->  a_dtable
 *  
 *  When argument is a number, this operation returns a copy of _dtable_ with each entry x replaced by x / _number_.
 *  When argument is a data array, this operation returns a copy of _dtable_ with each entry x replaced
 *  by x / the corresponding entry in the _other_ data array.
 */ VALUE dtable_div(VALUE ary, VALUE arg) {