make it possible to build with an earlier version of boost
make it possible to build with an earlier version of boost

kho/mr-cdec,kho/mr-cdec,pks/cdec-dtrain-legacy,pks/cdec-dtrain-legacy,pks/cdec-dtrain-legacy,kho/mr-cdec,kho/mr-cdec,pks/cdec-dtrain-legacy,pks/cdec-dtrain-legacy,kho/mr-cdec,pks/cdec-dtrain-legacy,kho/mr-cdec