Changes to Tcl between r3 and r4

'''Tool Command Language'''

Tcl is a dynamic programming language that is available on many platforms.

Some links:
   * http://www.tcl.tk/
   * http://wiki.tcl.tk/
----
'''Tcl Documentation'''
   * Tcl Cheat Sheet [http://home.houston.rr.com/brianohagan/tcl_tk_ref_guide.html] [http://www.rkeene.org/projects/info/resources/tcl/docs/tcl-tk-reference-guide.pdf]
   * Tcl Cheat Sheet [http://home.houston.rr.com/brianohagan/tcl_tk_ref_guide.html] (PDF [http://www.rkeene.org/projects/info/resources/tcl/docs/tcl-tk-reference-guide.pdf])

Legend

     Only in r3
     Only in r4
     -->      Modified slightly between r3 and r4