At the moment `alterCanIncludeInGoogleSitemap` is only called on other extensions, but really we'd want to see this called on the owner object and its extensions.
Fixed to use `invokeWithExtensions` rather than `extend`
Misc upgrade of module code so that site map.xml provides a index site map file based on the standards. Moved configuration vars to the Config API.
Considering how large a change this is, I've branched a 1.0 release off in github.
