Add revlog.parentrevs function.
This allows one to walk the revision graph using only revision numbers,
which can be faster than using revision hashes, especially for
RevlogNG, where the parents of a revision are stored as revision
numbers.
<div>
<a class="title" href="?cmd=changeset;node=#node#;style=gitweb"><span class="age">#date|age# ago</span>#desc|strip|firstline|escape#</a>
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<div class="title_text">
<div class="log_link">
<a href="?cmd=changeset;node=#node#;style=gitweb">changeset</a><br/>
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<i>#author|obfuscate# [#date|rfc822date#] rev #rev#</i><br/>
</div>
<div class="log_body">
#desc|strip|escape|addbreaks#
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<br/>
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