[plt-scheme] Extending

Hi all,

I spent some time reading around the codebase trying to discover the
best way to do two things:

1. Intercept the "Run" button press and do an additional action when
it is pressed, and
2. Add a drop-down menu widget to the button area.

#2 involves extending the frame mixin, doesn't it? If someone wouldn't
mind giving me a pointer in the right direction, I think it will speed
things up for me.

Many thanks,
Matt