DecimalContextTestCase: this permanently changed the

default decimal context, causing test_tokenize to fail
if it ran after test_contextlib.  Changed to restore
the decimal context in effect at the test's start.

Lib/test/test_contextlib.py

@@ -313,6 +313,8 @@ class DecimalContextTestCase(unittest.TestCase):
 
     def testBasic(self):
         ctx = decimal.getcontext()
+        orig_context = ctx.copy()
+        try:
             ctx.prec = save_prec = decimal.ExtendedContext.prec + 5
             with decimal.ExtendedContext:
                 self.assertEqual(decimal.getcontext().prec,
@@ -327,6 +329,8 @@ class DecimalContextTestCase(unittest.TestCase):
                 self.assertEqual(decimal.getcontext().prec, save_prec)
             else:
                 self.fail("Didn't raise ZeroDivisionError")
+        finally:
+            decimal.setcontext(orig_context)
 
 
 # This is needed to make the test actually run under regrtest.py!