[test.grid_provider_dgf] add files

dune/stuff/test/CMakeLists.txt

@@ -37,6 +37,11 @@ END_TESTCASES()
 
 # link grid files
 foreach (filename
-         "gmsh_2d_simplices.msh")
+         "gmsh_2d_simplices.msh"
+         "dgf_1d_interval.dgf"
+         "dgf_2d_interval.dgf"
+         "dgf_3d_interval.dgf"
+         "dgf_4d_interval.dgf"
+        )
   execute_process(COMMAND ln -s "${CMAKE_CURRENT_SOURCE_DIR}/${filename}" "${CMAKE_CURRENT_BINARY_DIR}/${filename}")
 endforeach (filename)