Have lookup-nodeset return a sequence of nodes

The function lookup-nodeset used to return a NodeList. This isn't very useful, so the xenopath.com/node-seq function was made public and lookup-nodeset is changed to call it. This was a problem for lookup, because it never called lookup-nodeset. The answer was to replace to-qname with get-lookup, which isntead of returning the proper QName object, it returns the proper lookup function. Now lookup simply gets the proper lookup function and invokes it.