/*
 *  call-seq:
 *     dtable.set_column(int,a_dvec) -> a_dvec
 *  
 *  Stores the contents of _a_dec_ in the specified column of the array.
 *  The length of the vector must equal the number of rows in the array.
 */ VALUE dtable_set_column(VALUE ary, VALUE col_num, VALUE dvec) {