hgweb: shorten all the URLs in the standard templates
A URL like this:
http://www.selenic.com/hg/?cmd=changeset;node=5010207c35273ac1331cae44c253dd41fa07cb7f
is now presented as:
http://www.selenic.com/hg/?cs=5010207c352
(though the old style still works, of course)