update version-check message in setup.py and IPython.__init__

clearer message that IPython no longer supports 2.6.

setup.py

@@ -26,12 +26,10 @@ import sys
 
 # This check is also made in IPython/__init__, don't forget to update both when
 # changing Python version requirements.
-#~ if sys.version[0:3] < '2.6':
-    #~ error = """\
-#~ ERROR: 'IPython requires Python Version 2.6 or above.'
-#~ Exiting."""
-    #~ print >> sys.stderr, error
-    #~ sys.exit(1)
+if sys.version_info[:2] < (2,7):
+    error = "ERROR: IPython requires Python Version 2.7 or above."
+    print(error, file=sys.stderr)
+    sys.exit(1)
 
 PY3 = (sys.version_info[0] >= 3)