Implementation of per-user .hgignore.
Reference: http://www.selenic.com/mercurial/bts/issue166
If the [ui] section of .hgrc contains keys like "ignore" or
"ignore.something", the values corresponding to these keys are
treated as per-user hgignore files. These hgignore files apply to all
repositories used by that user.
<item>
<title>#tag|escape#</title>
<link>#url#?cs=#node|short#</link>
<description><![CDATA[#tag|strip|escape|addbreaks#]]></description>
<pubDate>#date|rfc822date#</pubDate>
</item>