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/string.rst b/Doc/library/string.rst
index d785b7b..9ee81b5 100644
--- a/Doc/library/string.rst
+++ b/Doc/library/string.rst
@@ -7,6 +7,10 @@
 
 .. index:: module: re
 
+**Source code:** :source:`Lib/string.py`
+
+--------------
+
 The :mod:`string` module contains a number of useful constants and
 classes, as well as some deprecated legacy functions that are also
 available as methods on strings. In addition, Python's built-in string
@@ -17,12 +21,6 @@
 :ref:`string-formatting` section. Also, see the :mod:`re` module for
 string functions based on regular expressions.
 
-.. seealso::
-
-   Latest version of the `string module Python source code
-   <http://svn.python.org/view/python/branches/release27-maint/Lib/string.py?view=markup>`_
-
-
 String constants
 ----------------