added missing return in operator= which returns non-void

[[Imported from SVN: r2054]]

grid/common/entity.hh

@@ -464,7 +464,11 @@ namespace Dune
     /** hide copy constructor */
     Entity(const Entity& rhs) : realEntity(rhs.realEntity) {};
     /** hide assignement operator */
-    Entity & operator = (const Entity& rhs) { realEntity = rhs.realEntity; };
+    Entity & operator = (const Entity& rhs) {
+      realEntity = rhs.realEntity;
+      return *this;
+    }
+
   };
 
   /********************************************************************/