Major change in the internal structure of the Decimal

number: now it does not store the mantissa as a tuple
of numbers, but as a string.

This avoids a lot of conversions, and achieves a
speedup of 40%. The API remains intact.

Thanks Mark Dickinson.

Lib/test/test_decimal.py

@@ -464,6 +464,7 @@ class DecimalExplicitConstructionTest(unittest.TestCase):
         self.assertRaises(ValueError, Decimal, (1, (4, 3, 4, None, 1), 2) )
         self.assertRaises(ValueError, Decimal, (1, (4, -3, 4, 9, 1), 2) )
         self.assertRaises(ValueError, Decimal, (1, (4, 10, 4, 9, 1), 2) )
+        self.assertRaises(ValueError, Decimal, (1, (4, 3, 4, 'a', 1), 2) )
 
     def test_explicit_from_Decimal(self):