I'm trying to set up a callback for when the limits of an interactive
axes object, with an image plot, has its limits changed. The callback
itself is somewhat expensive, and the zooming procedure seems to
figure sequential events for each axis -- x and y -- that is changed.
This results in doubling up on the work that is done.
Is there a way to either suppress until the display itself is updated,
or to connect to a single event that gets called when both axes are