yelp-view: Fix page not found with anchor links

The second time you click an anchor link on the same page, you
will land at a page not found error.

Instead of expecting the anchor to appear after the base page
uri, yelp-view was expecting the anchor after the full
current uri. So on the second anchor click it was looking for
bogus-uri/page#anchor1#anchor2
instead of
bogus-uri/page#anchor2

Fixed things up so we check for relative anchor links against the
base page uri.

[endlessm/eos-shell#4233]