introduced _sick_ trick to get UG to build again: the macro

USING_UF_NAMESPACES in inherently broken, because it uses both the
dimensional and the undimensional namespace (which is _not_ what one
would expect of this macro!). In a sourcefile which does not include
any header needing a dimension this macro will break, because
UG2d/UG3d is not known. Now, a dummy namespace is created on each
call... :-(

[[Imported from SVN: r7727]]

low/namespace.h

@@ -62,12 +62,12 @@
 #ifdef _3
 #define START_UGDIM_NAMESPACE namespace UG3d {
 #define USING_UGDIM_NAMESPACE using namespace UG3d;
-#define USING_UG_NAMESPACES using namespace UG3d; using namespace UG;
+#define USING_UG_NAMESPACES namespace UG3d {}; using namespace UG3d; using namespace UG;
 #define NS_DIM_PREFIX UG3d::
 #else
 #define START_UGDIM_NAMESPACE namespace UG2d {
 #define USING_UGDIM_NAMESPACE using namespace UG2d;
-#define USING_UG_NAMESPACES using namespace UG2d; using namespace UG;
+#define USING_UG_NAMESPACES namespace UG2d {}; using namespace UG2d; using namespace UG;
 #define NS_DIM_PREFIX UG2d::
 #endif