Have attached debugger-ui.patch, which greatly updates the user interface for the existing debugger.  

This also relies on some images that should be downloaded and unpacked into the 'Icons' directory: http://www.tkdocs.com/images/debugicons.zip

Summary of changes:
 * works with both Tk 8.4 and 8.5+
 * paned window separates left and right, allowing adjusting relative sizes
 * on left, toolbar with graphical/text buttons, plus message, and stack
 * on right, local and global variables of selected stack frame
 * running program can be interrupted via 'stop' button
 * stack and variables use listbox (8.4) or tree (with resizable columns)
 * removed locals, globals, and stack 'view' options
 * source option changed to auto-open windows to see source
 * can always view source by double-clicking or context menu in stack
 * full value of variable can be seen via tooltip in variable list
 
In future, this will also replace the 'stack viewer' feature for displaying
exceptions, but this has not yet been integrated.