Enable doctest running for several other documents.
We have now over 640 doctests that are run with "make doctest".
diff --git a/Doc/library/weakref.rst b/Doc/library/weakref.rst
index 4f17c0c..2ca864f 100644
--- a/Doc/library/weakref.rst
+++ b/Doc/library/weakref.rst
@@ -243,7 +243,7 @@
----------------------
Weak reference objects have no attributes or methods, but do allow the referent
-to be obtained, if it still exists, by calling it::
+to be obtained, if it still exists, by calling it:
>>> import weakref
>>> class Object:
@@ -256,7 +256,7 @@
True
If the referent no longer exists, calling the reference object returns
-:const:`None`::
+:const:`None`:
>>> del o, o2
>>> print r()