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/cmd.rst b/Doc/library/cmd.rst
index b0508a3..ea24122 100644
--- a/Doc/library/cmd.rst
+++ b/Doc/library/cmd.rst
@@ -1,4 +1,3 @@
-
 :mod:`cmd` --- Support for line-oriented command interpreters
 =============================================================
 
@@ -6,17 +5,15 @@
    :synopsis: Build line-oriented command interpreters.
 .. sectionauthor:: Eric S. Raymond <esr@snark.thyrsus.com>
 
+**Source code:** :source:`Lib/cmd.py`
+
+--------------
 
 The :class:`Cmd` class provides a simple framework for writing line-oriented
 command interpreters.  These are often useful for test harnesses, administrative
 tools, and prototypes that will later be wrapped in a more sophisticated
 interface.
 
-.. seealso::
-
-   Latest version of the `cmd module Python source code
-   <http://svn.python.org/view/python/branches/release27-maint/Lib/cmd.py?view=markup>`_
-
 .. class:: Cmd([completekey[, stdin[, stdout]]])
 
    A :class:`Cmd` instance or subclass instance is a line-oriented interpreter