Add scripts for 4.3.1-1 tweak release

This tweak release has been made to fix one critical issue in the package
that will be used in the tutorial session hold during RSNA 2013.
See http://wiki.na-mic.org/Wiki/index.php/RSNA2013_Planning

The issue was related to the ChangeTracker extension.
See https://github.com/fedorov/ChangeTrackerPy/issues/14

To make the deployment of the package on the RSNA workstation easier, the
tweak release script will also expect the ChangeTrackerPy extension source
code (rev 2d7f8ee3) to be checked out in the
directory <CTEST_DASHBOARD_ROOT>/ChangeTrackerPy-4311.

It will allow the extension to be packaged as a "build-in" module. This is
done by specifying the path to the extension source directory passing the
option "Slicer_EXTENSION_SOURCE_DIRS" while configuring Slicer.


Finally, an other set of commits adding a generic mechanism for persisting
node references in .mrml files has been backported. See issue #3416
Backported commits are: r22698, r22699, r22701

It basically ensures that scene saved using the "Slicer trunk rev >= 22644"
could still be open using the latest stable 4.3.1-1.
For more details: http://na-mic.org/Mantis/view.php?id=3469#c10271