del_node method fixed. Some other methods added.
del_node method fixed. Some other methods added.

git-svn-id: 3e146768ded29dc87a1df450e29a6df8f44fcb0f@828 5eb3cf9a-c56f-4155-9a08-806ae8551a6d

coin-or/GiMPy,coin-or/GiMPy