Get rid of __context__, per the latest changes to PEP 343 and python-dev
discussion.
There are two places of documentation that still mention __context__:
Doc/lib/libstdtypes.tex -- I wasn't quite sure how to rewrite that without
spending a whole lot of time thinking about it; and whatsnew, which Andrew
usually likes to change himself.
diff --git a/Lib/test/test_contextlib.py b/Lib/test/test_contextlib.py
index 53f23b2..8d3dd1a 100644
--- a/Lib/test/test_contextlib.py
+++ b/Lib/test/test_contextlib.py
@@ -51,7 +51,7 @@
         @contextfactory
         def whee():
             yield
-        ctx = whee().__context__()
+        ctx = whee()
         ctx.__enter__()
         # Calling __exit__ should not result in an exception
         self.failIf(ctx.__exit__(TypeError, TypeError("foo"), None))
@@ -63,7 +63,7 @@
                 yield
             except:
                 yield
-        ctx = whoo().__context__()
+        ctx = whoo()
         ctx.__enter__()
         self.assertRaises(
             RuntimeError, ctx.__exit__, TypeError, TypeError("foo"), None
@@ -152,8 +152,6 @@
         def a():
             yield 1
         class b(object):
-            def __context__(self):
-                return self
             def __enter__(self):
                 return 2
             def __exit__(self, *exc_info):
@@ -341,12 +339,12 @@
         orig_context = ctx.copy()
         try:
             ctx.prec = save_prec = decimal.ExtendedContext.prec + 5
-            with decimal.ExtendedContext:
+            with decimal.ExtendedContext.context_manager():
                 self.assertEqual(decimal.getcontext().prec,
                                  decimal.ExtendedContext.prec)
             self.assertEqual(decimal.getcontext().prec, save_prec)
             try:
-                with decimal.ExtendedContext:
+                with decimal.ExtendedContext.context_manager():
                     self.assertEqual(decimal.getcontext().prec,
                                      decimal.ExtendedContext.prec)
                     1/0