Backport source links from 3.x.

Existing links have been updated to use the new reST role.  In some
files, I have also made cosmetic changes to the header.
diff --git a/Doc/library/cookielib.rst b/Doc/library/cookielib.rst
index 4ca0471..77d6624 100644
--- a/Doc/library/cookielib.rst
+++ b/Doc/library/cookielib.rst
@@ -11,10 +11,11 @@
    Python 3.0.  The :term:`2to3` tool will automatically adapt imports when
    converting your sources to 3.0.
 
-
 .. versionadded:: 2.4
 
+**Source code:** :source:`Lib/cookielib.py`
 
+--------------
 
 The :mod:`cookielib` module defines classes for automatic handling of HTTP
 cookies.  It is useful for accessing web sites that require small pieces of data