Make xrange more Py_ssize_t aware, by assuming a Py_ssize_t is always at
least as big as a long. I believe this to be a safe assumption that is being
made in many parts of CPython, but a check could be added.

len(xrange(sys.maxint)) works now, so fix the testsuite's odd exception for
64-bit platforms too. It also fixes 'zip(xrange(sys.maxint), it)' as a
portable-ish (if expensive) alternative to enumerate(it); since zip() now
calls len(), this was breaking on (real) 64-bit platforms. No additional
test was added for that behaviour.
diff --git a/Lib/test/test_xrange.py b/Lib/test/test_xrange.py
index 9f9daa7..eafb7fa 100644
--- a/Lib/test/test_xrange.py
+++ b/Lib/test/test_xrange.py
@@ -54,12 +54,7 @@
         self.assertRaises(OverflowError, xrange, 0, 2*sys.maxint)
 
         r = xrange(-sys.maxint, sys.maxint, 2)
-        if sys.maxint > 0x7fffffff:
-            # XXX raising ValueError is less than ideal, but this can't
-            # be fixed until range_length() returns a long in rangeobject.c
-            self.assertRaises(ValueError, len, r)
-        else:
-            self.assertEqual(len(r), sys.maxint)
+        self.assertEqual(len(r), sys.maxint)
         self.assertRaises(OverflowError, xrange, -sys.maxint-1, sys.maxint, 2)
 
 def test_main():