setup: drop support for Python 2.6 (BC)

setup: drop support for Python 2.6 (BC)

Per discussion on the mailing list and elsewhere, we've decided that
Python 2.6 is too old to continue supporting. We keep accumulating
hacks/fixes/workarounds for 2.6 and this is taking time away from
more important work.

So with this patch, we officially drop support for Python 2.6 and
require Python 2.7 to run Mercurial.

--- a/contrib/debian/control	Sat May 06 11:16:59 2017 -0700
+++ b/contrib/debian/control	Tue May 02 16:19:04 2017 -0700
@@ -12,7 +12,7 @@
  unzip,
  zip
 Standards-Version: 3.9.4
-X-Python-Version: >= 2.6
+X-Python-Version: >= 2.7
 
 Package: mercurial
 Depends:

--- a/contrib/mercurial.spec	Sat May 06 11:16:59 2017 -0700
+++ b/contrib/mercurial.spec	Tue May 02 16:19:04 2017 -0700
@@ -37,8 +37,8 @@
 %if "%{?withpython}"
 BuildRequires: readline-devel, openssl-devel, ncurses-devel, zlib-devel, bzip2-devel
 %else
-BuildRequires: python >= 2.6, python-devel, python-docutils >= 0.5
-Requires: python >= 2.6
+BuildRequires: python >= 2.7, python-devel, python-docutils >= 0.5
+Requires: python >= 2.7
 %endif
 # The hgk extension uses the wish tcl interpreter, but we don't enforce it
 #Requires: tk

--- a/setup.py	Sat May 06 11:16:59 2017 -0700
+++ b/setup.py	Tue May 02 16:19:04 2017 -0700
@@ -5,8 +5,8 @@
 # 'python setup.py --help' for more options
 
 import sys, platform
-if sys.version_info < (2, 6, 0, 'final'):
-    raise SystemExit("Mercurial requires Python 2.6 or later.")
+if sys.version_info < (2, 7, 0, 'final'):
+    raise SystemExit('Mercurial requires Python 2.7 or later.')
 
 if sys.version_info[0] >= 3:
     printf = eval('print')