get_node_attr() nad get_edge_attr() methods added.
get_node_attr() nad get_edge_attr() methods added.

git-svn-id: 3e146768ded29dc87a1df450e29a6df8f44fcb0f@811 5eb3cf9a-c56f-4155-9a08-806ae8551a6d

coin-or/GiMPy,coin-or/GiMPy