Replace occurrences of '\d' with '[0-9]' in Decimal regex, to make sure

that the behaviour of Decimal doesn't change if/when re.UNICODE becomes
assumed in Python 3.0.

Also add a check that alternative Unicode digits (e.g. u'\N{FULLWIDTH
DIGIT ONE}') are *not* accepted in a numeric string.

Lib/test/test_decimal.py

@@ -432,6 +432,9 @@ class DecimalExplicitConstructionTest(unittest.TestCase):
         self.assertEqual(str(Decimal(u'-Inf')), '-Infinity')
         self.assertEqual(str(Decimal(u'NaN123')), 'NaN123')
 
+        #but alternate unicode digits should not
+        self.assertEqual(str(Decimal(u'\uff11')), 'NaN')
+
     def test_explicit_from_tuples(self):
 
         #zero