make hgweb use new archival module.
also use "x-gzip" encoding for ".tar.gz" files, so mozilla and firefox
will not transparently decompress stream and save with wrong name.
<item>
<title>#desc|strip|firstline|strip|escape#</title>
<link>#url#?f=#filenode|short#;file=#file|urlescape#</link>
<description><![CDATA[#desc|strip|escape|addbreaks#]]></description>
<author>#author|obfuscate#</author>
<pubDate>#date|rfc822date#</pubDate>>
</item>