Enforce python 2.6 or later.

git_cl.py

 #!/usr/bin/env python
 # Copyright (c) 2012 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 # Copyright (C) 2008 Evan Martin <martine@danga.com>
 
 """A git-command for integrating reviews on Rietveld."""
 
 import logging
@@ skipping 1369 matching lines @@
     command = '<command>'
   else:
     # OptParser.description prefer nicely non-formatted strings.
     parser.description = re.sub('[\r\n ]{2,}', ' ', obj.__doc__)
   parser.set_usage('usage: %%prog %s [options] %s' % (command, more))
 
 
 def main(argv):
   """Doesn't parse the arguments here, just find the right subcommand to
   execute."""
+  if sys.hexversion < 0x02060000:
+    print >> sys.stderr, (
+        '\nYour python version %s is unsupported, please upgrade.\n' %
+        sys.version.split(' ', 1)[0])
+    return 2
   # Reload settings.
   global settings
   settings = Settings()
 
   # Do it late so all commands are listed.
   CMDhelp.usage_more = ('\n\nCommands are:\n' + '\n'.join([
       '  %-10s %s' % (fn[3:], Command(fn[3:]).__doc__.split('\n')[0].strip())
       for fn in dir(sys.modules[__name__]) if fn.startswith('CMD')]))
 
   # Create the option parse and add --verbose support.
@@ skipping 28 matching lines @@
              'and retry or visit go/isgaeup.\n%s') % (e.code, str(e)))
 
   # Not a known command. Default to help.
   GenUsage(parser, 'help')
   return CMDhelp(parser, argv)
 
 
 if __name__ == '__main__':
   fix_encoding.fix_encoding()
   sys.exit(main(sys.argv[1:]))