figures are not closed in a notebook...

I really like the %matplotlib widget extension for the interactivity it provides. However, the transition from %matplotlib inline to widget is not as smooth as I hoped for:

- every cell that does some plotting should open a new figure (else a figure from a previously executed cell will be used)
- when you reexecute a cell (often done in notebooks, meant for prototyping and education...) a new figure is made AND THE OLD ONE IS KEPT... shouldn't the old figure be removed/closed to stay in line with the inline matplotlib option?

Regards
Rein van den Boomgaard

Reproduce the behavior in a notebook using %matplotlib widget, comparing fresh and re-executed plotting cells with %matplotlib inline. Done means each plotting cell gets the expected figure and re-executing it does not leave the prior figure open; trace the widget entry point from this reproduction to identify the relevant code and regression coverage.

Written by the indexing model from the issue text.