Tk-LabPopEntry-0.03

The LabPopEntry (short for Labeled PopEntry, in case you were wondering), is
simply a labeled version of my PopEntry widget.

It is quite a bit different internally from PopEntry, however.  It is derived
from the LabEntry widget, which is itself a frame based widget.  PopEntry was
derived from the Entry widget.

First, I had to dig out the subwidget references for the Entry widget,
and in some cases, test to make sure that I had the parent and not the Entry
widget itself.

Second, I decided to bind the Entry widget to the 'Key' event descriptor,
rather than overload the 'insert' method, as I did with PopEntry.  This saved
time and energy in the long run, and the effect was the same.

Third, I changed some method names to my liking, and made a slight 
modification to the configuration of the 'Sel. All' button.

Last, I Advertise()'d the toplevel popup menu so that it could be configured
directly.  I will ultimately include this in PopEntry as well, but it was
much easier the way I did it here.