revlog: reduce memory usage in addgroup - use a buffer to extract the delta from a chunk - avoid concatenating to a compressed delta - use a buffer to directly extra full text from a trivial delta - delete chunk and delta objects after use

#motd#
<div class="logo">
powered by<br/>
<a href="http://www.selenic.com/mercurial/">mercurial</a>
</div>

</body>
</html>