CTree child of node

[Samuel Solon <ssolon usa net>]

There doesn't seem to be any way to get the child of a node (at least none
that I can find but perhaps I misunderstand the intended use of nodes).

Assuming that the GTK_CTREE_xxx macros are intended to be used for direct
access to the structure I would propose the following:

#define GTK_CTREE_NODE_CHILD(_node_) (GTK_CTREE_ROW(_node_)->children)

IMHO is would also be nice to have GTK_CTREE_NODE_SIBLING and
GTK_CTREE_NODE_PARENT macros also.