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>#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>