Added check for minimal python version to setup.py

Added check for minimal python version to setup.py

--- a/setup.py	Thu Mar 09 16:27:21 2006 -0800
+++ b/setup.py	Fri Mar 10 10:44:17 2006 +0100
@@ -5,8 +5,11 @@
 # './setup.py install', or
 # './setup.py --help' for more options
 
+import sys
+if not hasattr(sys, 'version_info') or sys.version_info < (2, 3):
+    raise SystemExit, "Mercurial requires python 2.3 or later."
+
 import glob
-import sys
 from distutils.core import setup, Extension
 from distutils.command.install_data import install_data