branchmap: fix python 2.6 by using util.buffer() instead of passing bytearray

mercurial/branchmap.py

@@ -408,7 +408,8 b' class revbranchcache(object):'
 
         # fast path: extract data from cache, use it if node is matching
         reponode = changelog.node(rev)[:_rbcnodelen]
-        cachenode, branchidx = unpack_from(_rbcrecfmt, self._rbcrevs, rbcrevidx)
+        cachenode, branchidx = unpack_from(
+            _rbcrecfmt, util.buffer(self._rbcrevs), rbcrevidx)
         close = bool(branchidx & _rbccloseflag)
         if close:
             branchidx &= _rbcbranchidxmask