Enforce python 2.6 or later.

gcl.py

Index: gcl.py
diff --git a/gcl.py b/gcl.py
index 86dc43917e354f38813d5fe127690a179dc48890..78880048942065b27ca4ded829d732f60f700b5b 100755
--- a/gcl.py
+++ b/gcl.py
@@ -1418,9 +1418,11 @@ def CMDhelp(args):
 
 
 def main(argv):
-  if sys.hexversion < 0x02050000:
+  if sys.hexversion < 0x02060000:
     print >> sys.stderr, (
-        '\nYour python version is unsupported, please upgrade.\n')
+        '\nYour python version %s is unsupported, please upgrade.\n' %
+        sys.version.split(' ', 1)[0])
+    return 2
   if not argv:
     argv = ['help']
   command = Command(argv[0])