Added a warning. Please merge to relase.

[[Imported from SVN: r1579]]

dune/istl/paamg/parameters.hh

@@ -394,6 +394,7 @@ namespace Dune
        * @brief Set the debugging level.
        *
        * @param level If 0 no debugging output will be generated.
+       * @warning In parallel the level has to be consistent over all procceses.
        */
       void setDebugLevel(int level)
       {