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.

 EXTRA_DIST += \

 	demo/CMakeLists.txt \

 	demo/digraph.lgf

 if WANT_DEMO

 noinst_PROGRAMS += \

 	demo/arg_parser_demo \

 	demo/graph_to_eps_demo \

 	demo/lgf_demo

 endif WANT_DEMO

 demo_arg_parser_demo_SOURCES = demo/arg_parser_demo.cc

 demo_graph_to_eps_demo_SOURCES = demo/graph_to_eps_demo.cc

 demo_lgf_demo_SOURCES = demo/lgf_demo.cc