Got rid of useless "Welcome" screen.
Folded Tcl/Tk into the main Python component.
Bug introduced during upgrade:  Start Menu entries didn't work if
    installation was to a path with an embedded space, because the
    enclosing quotes somehow got dropped on the cmdline args.  Repaired.
Years of wizard-generated code blocks left this script hard to read.
    Added many more comments, blank lines, and rearranged related code
    into related blocks where they had drifted apart.
Added %_PYMAJOR_% and %_PYMINOR_% compiler vrbls, and reworked script
    items to use them as appropriate.  This should slash the amount of
    hand-fiddling needed when version numbers change.  Indeed, in the
    body of the script, only the first line should need changing now.
Deleted unreferenced wizard-generated compiler vrbls.