Undirected graph documentation and concept refinements.
* quite a few bug fixes
* concept::UndirGraph is almost complete and looks quite good.
1 * ValueType -> Value, KeyType -> Key, ReferenceType ->Reference,
3 * target() -> target(), source() -> source()
5 * Right include paths in documentation
7 2004-09-30 Alpar Juttner <alpar@cs.elte.hu>