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/sched.rst b/Doc/library/sched.rst
index 1efe47a..824df04 100644
--- a/Doc/library/sched.rst
+++ b/Doc/library/sched.rst
@@ -7,14 +7,13 @@
 
 .. index:: single: event scheduling
 
+**Source code:** :source:`Lib/sched.py`
+
+--------------
+
 The :mod:`sched` module defines a class which implements a general purpose event
 scheduler:
 
-.. seealso::
-
-   Latest version of the `sched module Python source code
-   <http://svn.python.org/view/python/branches/release27-maint/Lib/sched.py?view=markup>`_
-
 .. class:: scheduler(timefunc, delayfunc)
 
    The :class:`scheduler` class defines a generic interface to scheduling events.