[PATCH 2 of 6 V2] perf: define util.safehasattr forcibly for Mercurial earlier than 1.9.3

[FUJIWARA Katsunori]

# HG changeset patch
# User FUJIWARA Katsunori <foozy at lares.dti.ne.jp>
# Date 1467671151 -32400
#      Tue Jul 05 07:25:51 2016 +0900
# Node ID bb7723a5b052c2169498e568a671f46ec7a82ae4
# Parent  121d38c22d5a11fc793aae9f3919371c9eb1f6b7
perf: define util.safehasattr forcibly for Mercurial earlier than 1.9.3

Before this patch, using util.safehasattr() prevents perf.py from
being loaded by Mercurial earlier than 1.9.3 (or 94b200a11cf7),
because util.safehasattr() isn't available in such Mercurial, even
though there are some code paths for Mercurial earlier than 1.9.3.

For example, setting "_prereadsize" attribute in perfindex() and
perfnodelookup() is effective only with Mercurial earlier than 1.8 (or
61c9bc3da402).

This patch is a preparation for using util.safehasattr() safely in
subsequent patches.

This patch defines util.safehasattr() forcibly without examining
whether it is available or not, because:

  - examining existence of "safehasattr" safely itself needs similar logic
  - safehasattr() is small enough to define locally

diff --git a/contrib/perf.py b/contrib/perf.py
--- a/contrib/perf.py
+++ b/contrib/perf.py
@@ -39,6 +39,14 @@ from mercurial import (
     util,
 )
 
+# for "historical portability":
+# define util.safehasattr forcibly, because util.safehasattr has been
+# available since 1.9.3 (or 94b200a11cf7)
+_undefined = object()
+def safehasattr(thing, attr):
+    return getattr(thing, attr, _undefined) is not _undefined
+setattr(util, 'safehasattr', safehasattr)
+
 formatteropts = commands.formatteropts
 revlogopts = commands.debugrevlogopts