mercurial.el: deal with more vagaries of "hg status".
If we run "hg status" on a file that does not exist, it prints an error
message. Attempt to extract the name of the file.
<table class="slogEntry parity#parity#">
<tr>
<td class="age">#date|age#</td>
<td class="author">#author|obfuscate#</td>
<td class="node"><a href="?cs=#node|short#">#desc|strip|firstline|escape#</a></td>
</tr>
</table>