[gdome] add listeners field to libxml tree.h?

[Raph Levien <raph acm org>]

This is primarily a question for Daniel.

We need to implement event listeners pretty soon in Gdome. The easiest
thing to do is to add a "listeners" field to every major node struct
in libxml's trees.

If this is voted to be not a good idea, then the next best choice is
probably to implement a hashtable mapping nodes to listeners. This is
actually more memory efficient, but otoh adds quite a bit of overhead
to mutations -- you have to walk up the tree to the root, doing a
hashtable lookup for each node.

What's the right thing to do here?

Raph