help: fix column alignment in "hg help" output
The output of "hg help" is changed to ensure that the column containing
descriptions of commands, extensions, and other topics is correctly alignmened.
<tr class="parity{parity}">
<td class="age">{date|rfc822date}</td>
<td class="author">{author|person}</td>
<td class="description"><a href="{url}rev/{node|short}{sessionvars%urlparameter}">{desc|strip|firstline|escape|nonempty}</a>{inbranch%changelogbranchname}{branches%changelogbranchhead}{tags % '<span class="tag">{name|escape}</span> '}{bookmarks % '<span class="tag">{name|escape}</span> '}</td>
</tr>