[PATCH STABLE] setup: drop use of set literal so parsable on Python 2.6

[Yuya Nishihara]

# HG changeset patch
# User Yuya Nishihara <yuya at tcha.org>
# Date 1501079982 -32400
#      Wed Jul 26 23:39:42 2017 +0900
# Branch stable
# Node ID aee0559d75bf2d5d0802acd98a4867fcdf885469
# Parent  025017423e532037e470e3e5e9b845cba5c4e710
setup: drop use of set literal so parsable on Python 2.6

Otherwise friendly error wouldn't be displayed.

diff --git a/setup.py b/setup.py
--- a/setup.py
+++ b/setup.py
@@ -576,7 +576,7 @@ class hginstall(install):
         # Screen out egg related commands to prevent egg generation.  But allow
         # mercurial.egg-info generation, since that is part of modern
         # packaging.
-        excl = {'bdist_egg'}
+        excl = set(['bdist_egg'])
         return filter(lambda x: x not in excl, install.get_sub_commands(self))
 
 class hginstalllib(install_lib):