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/linecache.rst b/Doc/library/linecache.rst
index 8ebee05..39385f9 100644
--- a/Doc/library/linecache.rst
+++ b/Doc/library/linecache.rst
@@ -6,17 +6,15 @@
    :synopsis: This module provides random access to individual lines from text files.
 .. sectionauthor:: Moshe Zadka <moshez@zadka.site.co.il>
 
+**Source code:** :source:`Lib/linecache.py`
+
+--------------
 
 The :mod:`linecache` module allows one to get any line from any file, while
 attempting to optimize internally, using a cache, the common case where many
 lines are read from a single file.  This is used by the :mod:`traceback` module
 to retrieve source lines for inclusion in  the formatted traceback.
 
-.. seealso::
-
-   Latest version of the `linecache module Python source code
-   <http://svn.python.org/view/python/branches/release27-maint/Lib/linecache.py?view=markup>`_
-
 The :mod:`linecache` module defines the following functions: