OpenMesh/Core/Utils/PropertyManager: Added property to retain() method.

git-svn-id: http://www.openmesh.org/svnrepo/OpenMesh/trunk@670 fdac6126-5c0c-442c-9429-916003d36597

src/OpenMesh/Core/Utils/PropertyManager.hh

@@ -151,8 +151,8 @@ class PropertyManager {
          * If this method is called, the encapsulated property will not be deleted
          * upon destruction of the PropertyManager instance.
          */
-        inline void retain() {
-            retain_ = true;
+        inline void retain(bool doRetain = true) {
+            retain_ = doRetain;
         }
 
         /**