Greatly extend and improve the test file for adaptors (#67)

- Add concept checks for the alterable, extendable, erasable
and clearable adaptors.
- Add test cases for modifying the underlying graphs through adaptors
whenever it is possible.
- Check the conversions between Node, Arc and Edge types.
- Add more test cases for the adaptor-specific functions and maps:
enable(), disable(), status(), forward(), backward(), CombinedArcMap,
CombinedNodeMap, ResidualCapacity etc.
- Use checkGraphIncEdgeArcLists() to simplify the test cases for
undirected graphs.
- Add test cases that use static graph structure (GridGraph) with
several adaptors combined.
- Add comments for the test cases.

 INCLUDE_DIRECTORIES(${CMAKE_SOURCE_DIR})

 LINK_DIRECTORIES(${CMAKE_BINARY_DIR}/lemon)

 SET(TESTS

   bfs_test

   circulation_test

   counter_test

   dfs_test

   digraph_test

   dijkstra_test

   dim_test

   error_test

   graph_adaptor_test

   graph_copy_test

   graph_test

   graph_utils_test

   hao_orlin_test

   heap_test

   kruskal_test

   maps_test

   max_matching_test

   radix_sort_test

   path_test

   preflow_test

   random_test

   suurballe_test

   time_measure_test

   unionfind_test)

 FOREACH(TEST_NAME ${TESTS})

   ADD_EXECUTABLE(${TEST_NAME} ${TEST_NAME}.cc)

   TARGET_LINK_LIBRARIES(${TEST_NAME} lemon)

   ADD_TEST(${TEST_NAME} ${TEST_NAME})

 ENDFOREACH(TEST_NAME)