[PATCH 7 of 9 py3 v3] branchmap: don't use buffer() on Python 3

[Augie Fackler]

# HG changeset patch
# User Augie Fackler <augie at google.com>
# Date 1489297759 18000
#      Sun Mar 12 00:49:19 2017 -0500
# Node ID 46eb1834c644e675bd246bbae254cada40c2f21b
# Parent  85be2e7b95aac78211a83d71e14ff8a6901ebbd5
branchmap: don't use buffer() on Python 3

This is certainly slower than the Python 2 code, but it works, and we
can revisit it later if it's a problem.

diff --git a/mercurial/branchmap.py b/mercurial/branchmap.py
--- a/mercurial/branchmap.py
+++ b/mercurial/branchmap.py
@@ -409,7 +409,7 @@ class revbranchcache(object):
         # fast path: extract data from cache, use it if node is matching
         reponode = changelog.node(rev)[:_rbcnodelen]
         cachenode, branchidx = unpack(
-            _rbcrecfmt, buffer(self._rbcrevs, rbcrevidx, _rbcrecsize))
+            _rbcrecfmt, util.buffer(self._rbcrevs, rbcrevidx, _rbcrecsize))
         close = bool(branchidx & _rbccloseflag)
         if close:
             branchidx &= _rbcbranchidxmask