backout: allow backout of merge changeset with --parent option.
--parent allows to choose which parent of merge to revert to.
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<title>Mercurial repositories index</title>
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<h2>Mercurial Repositories</h2>
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<td><a href="?sort=#sort_name#">Name</a></td>
<td><a href="?sort=#sort_description#">Description</a></td>
<td><a href="?sort=#sort_contact#">Contact</a></td>
<td><a href="?sort=#sort_lastchange#">Last change</a></td>
<td> </td>
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