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.

contrib/debian/control

@@ -12,7 +12,7 b' Build-Depends:'
  unzip,
  zip
 Standards-Version: 3.9.4
-X-Python-Version: >= 2.6
+X-Python-Version: >= 2.7
 
 Package: mercurial
 Depends:

contrib/mercurial.spec

@@ -37,8 +37,8 b' BuildRequires: make, gcc, gettext'
 %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

setup.py

@@ -5,8 +5,8 b''
 # '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')