In `general' there is no relationship between two similar urls

	freddy://bounce/

However in practice

	when 

	http://hostname/directory/

	moves

	http://hostname/directory/file

	moves with it (directory and file are just arbitrary names
for parts of the URL chosen for no reason whatsoever)

To detect this kind of change, we should btree index the links, then 

	if we find a broken link, we should check to see if any links
	share a common root with it, then check those links also

	if we have a `directory' link moving, then we should decide whether
	to move other links related.