add method top_and_pop_back() for them speed freaks

[[Imported from SVN: r6547]]

dune/common/reservedvector.hh

@@ -89,6 +89,12 @@ namespace Dune
       if (! empty()) sz--;
     }
 
+    //! Erases the last element of the vector, and returns it
+    T top_and_pop_back()
+    {
+      return data[--sz];
+    }
+
     //! Returns a iterator pointing to the beginning of the vector.
     iterator begin(){
       return iterator(*this, 0);