convert: fix test-convert-svn-* problems with mtime not changing
The `svn commit` command does not detect changed files unless
their mtime has changed. A quick succession of, for instance,
`svn co ...; echo x >> y; svn ci` can thus lead to the change to y
being ignored.
Edited by pmezard to write in binary mode.
<item>
<title>#desc|strip|firstline|strip|escape#</title>
<link>{urlbase}{url}rev/{node|short}</link>
<description><![CDATA[#desc|strip|escape|addbreaks#]]></description>
<author>#author|obfuscate#</author>
<pubDate>#date|rfc822date#</pubDate>
</item>