hgweb: don't dereference symbolic revision in spartan style
Let's make spartan templates use symbolic revision in navigation links.
The majority of links (log, filelog, annotate, etc) still use node hashes, and
many pages also have permanent link to current node hash (i.e. you can go from
/rev/tip to /rev/<tip hash> without manual url editing), so it's safe to
update navigation.
Testing that hghave does not crash when checking features
$ hghave --test-features 2>/dev/null