Check for at least having a final release of python 2.3.0 in setup.py

Mercurial uses features that are not in 2.3a1.

setup.py

@@ -6,7 +6,7 b''
 # './setup.py --help' for more options
 
 import sys
-if not hasattr(sys, 'version_info') or sys.version_info < (2, 3):
+if not hasattr(sys, 'version_info') or sys.version_info < (2, 3, 0, 'final'):
     raise SystemExit, "Mercurial requires python 2.3 or later."
 
 import os