- Display "(None)" (or text of your choosing) when empty.
- Don't set the focus.

Much has changed -- too much, in fact, to write down.
The big news is that there's a standard way to write IDLE extensions;
see extend.txt.  Some sample extensions have been provided, and
some existing code has been converted to extensions.  Probably the
biggest new user feature is a new search dialog with more options,
search and replace, and even search in files (grep).

This is exactly as downloaded from my laptop after returning
from the holidays -- it hasn't even been tested on Unix yet.

method browser into a separate class in its own module.