setup: Don't explicitly check for supported versions

With pypy3 advertising itself as py3.2, but still behaving like py3.3,
the check started to become awkward.  Plus, it seems to be nicer to
ask for forgiveness rather than permission.

setup.py

@@ -1,16 +1,17 @@
 # -*- coding: utf-8 -*-
 
-import sys
-if sys.version_info < (2, 6) or (3,) <= sys.version_info < (3, 3):
-    print("Babel requires Python 2.6, 2.7 or 3.3+")
-    sys.exit(1)
-
-
 import os
 import subprocess
+import sys
+
 from setuptools import setup
 
-from babel import __version__
+try:
+    from babel import __version__
+except SyntaxError as exc:
+    sys.stderr.write("Unable to import Babel (%s). Are you running a supported version of Python?\n" % exc)
+    sys.exit(1)
+
 
 sys.path.append(os.path.join('doc', 'common'))
 try: