make compile with gcc-3.4

(though this should also occur for later versions, if this implementation would ever be used)

[[Imported from SVN: r5891]]

dune/common/shared_ptr.hh

@@ -133,6 +133,7 @@ namespace Dune
     class PointerRep
     {
       friend class shared_ptr<element_type>;
+    protected:
       /** @brief The number of references. */
       int count_;
       /** @brief The representative. */