Fix traceback when nothing was added during unbundle
The changegroup and commit hook are now run only when
something is modified.
The correct number of changesets added is printed.
<item>
<title>#desc|firstline|escape#</title>
<link>#url#?cmd=changeset;node=#node#</link>
<description><![CDATA[#desc|escape|addbreaks#]]></description>
<author>#author|obfuscate#</author>
<pubDate>#date|rfc822date#</pubDate>
</item>