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/trace.rst b/Doc/library/trace.rst
index 2e9d2b4..a2afda1 100644
--- a/Doc/library/trace.rst
+++ b/Doc/library/trace.rst
@@ -1,21 +1,18 @@
-
 :mod:`trace` --- Trace or track Python statement execution
 ==========================================================
 
 .. module:: trace
    :synopsis: Trace or track Python statement execution.
 
+**Source code:** :source:`Lib/trace.py`
+
+--------------
 
 The :mod:`trace` module allows you to trace program execution, generate
 annotated statement coverage listings, print caller/callee relationships and
 list functions executed during a program run.  It can be used in another program
 or from the command line.
 
-.. seealso::
-
-   Latest version of the `trace module Python source code
-   <http://svn.python.org/view/python/branches/release27-maint/Lib/trace.py?view=markup>`_
-
 .. _trace-cli:
 
 Command-Line Usage