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/textwrap.rst b/Doc/library/textwrap.rst
index 8fbfe9c..84e6ee1 100644
--- a/Doc/library/textwrap.rst
+++ b/Doc/library/textwrap.rst
@@ -1,4 +1,3 @@
-
 :mod:`textwrap` --- Text wrapping and filling
 =============================================
 
@@ -7,20 +6,18 @@
 .. moduleauthor:: Greg Ward <gward@python.net>
 .. sectionauthor:: Greg Ward <gward@python.net>
 
-
 .. versionadded:: 2.3
 
+**Source code:** :source:`Lib/textwrap.py`
+
+--------------
+
 The :mod:`textwrap` module provides two convenience functions, :func:`wrap` and
 :func:`fill`, as well as :class:`TextWrapper`, the class that does all the work,
 and a utility function  :func:`dedent`.  If you're just wrapping or filling one
 or two  text strings, the convenience functions should be good enough;
 otherwise,  you should use an instance of :class:`TextWrapper` for efficiency.
 
-.. seealso::
-
-   Latest version of the `textwrap module Python source code
-   <http://svn.python.org/view/python/branches/release27-maint/Lib/textwrap.py?view=markup>`_
-
 .. function:: wrap(text[, width[, ...]])
 
    Wraps the single paragraph in *text* (a string) so every line is at most *width*