small fix :*

libwccl/variables.h

@@ -208,7 +208,7 @@ public:
 	 * shared pointers themselves cannot, use put etc. for that.
 	 */
 	template<typename T>
-	const typename detail::Vmap<T>::map_t get_all() const {
+	const typename detail::Vmap<T>::map_t& get_all() const {
 		BOOST_MPL_ASSERT(( boost::mpl::count<types, T> ));
 		return detail::Vmap<T>::map_;
 	}