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)
<item>
<title>#desc|firstline|escape#</title>
<link>#url#?cs=#node|short#</link>
<description><![CDATA[#desc|escape|addbreaks#]]></description>
<author>#author|obfuscate#</author>
<pubDate>#date|rfc822date#</pubDate>
</item>