Fixes for push corner case
TAH found a bug where push would push things the remote already had,
raising an assertion. This turned out to be because the changeset
protocol was not recording a common subset node in one case.
Also discovered was that the protocol was queueing multiple copies of
a node for pull. Fixed by changing fetch to a hash.
Add some more debugging output.
<item>
<title>#desc|firstline|escape#</title>
<link>#url#?cmd=file;file=#file#;filenode=#filenode#</link>
<description><![CDATA[#desc|escape|addbreaks#]]></description>
<author>#author|obfuscate#</author>
<pubDate>#date|rfc822date#</pubDate>>
</item>