Support for tree/hierarchy-based Traverse::xpath instead of index-based xpath

[lwu]

See http://earthcode.com/blog/2007/05/hpricot_georss_kml.html

and also Alexy's email request:

"When trying to call .xpath on certain nodes of a special leaf kind leaf, instead of a hierarchical path, I get something like,

//part[@id='16320']/leaf

leaf nodes hang off parents of node type 'part'. Those, in turn, hang of other nodes. Instead of a hierarchical path from root, Hpricot gives me the above king of index.

I'd like to get, for a given node, just the ancestors, directly to the root. How can I do that with Hpricot?"