From: Zbigniew Diaczyszyn on
I had not thought through the issue: The if condition tells the Linux
Tcl/Tk at runtime not to compile this procedure and therefore the
unknown namespace is no problem. And if the programm is executed on a
Mac then the procedure will be successfully compiled because wish on the
Mac knows the namespace.

Thank you, Kevin, for the hint. I compiled the program on a Linux host
with tclkit-darwin-aqua ... and I've got the preferences in the menu :-)))