Preliminary support for "from __future__ import generators" to enable
the yield statement.  I figure we have to have this in before I can
release 2.2a1 on Wednesday.

Note: test_generators is currently broken, I'm counting on Tim to fix
this.
diff --git a/Lib/__future__.py b/Lib/__future__.py
index 8510ceb..65416ae 100644
--- a/Lib/__future__.py
+++ b/Lib/__future__.py
@@ -67,3 +67,4 @@
                             `self.getMandatoryRelease()` + ")"
 
 nested_scopes = _Feature((2, 1, 0, "beta", 1), (2, 2, 0, "alpha", 0))
+generators = _Feature((2, 2, 0, "alpha", 1), (2, 3, 0, "final", 0))