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/filecmp.rst b/Doc/library/filecmp.rst
index 699e510..25d0701 100644
--- a/Doc/library/filecmp.rst
+++ b/Doc/library/filecmp.rst
@@ -1,4 +1,3 @@
-
 :mod:`filecmp` --- File and Directory Comparisons
 =================================================
 
@@ -6,16 +5,14 @@
    :synopsis: Compare files efficiently.
 .. sectionauthor:: Moshe Zadka <moshez@zadka.site.co.il>
 
+**Source code:** :source:`Lib/filecmp.py`
+
+--------------
 
 The :mod:`filecmp` module defines functions to compare files and directories,
 with various optional time/correctness trade-offs. For comparing files,
 see also the :mod:`difflib` module.
 
-.. seealso::
-
-   Latest version of the `filecmp Python source code
-   <http://svn.python.org/view/python/branches/release27-maint/Lib/filecmp.py?view=markup>`_
-
 The :mod:`filecmp` module defines the following functions: