Commit 8537e32

Interactive timers keep to their interval

Repeating timers created with `.FigureCanvasBase.new_timer` now fire on the

interval they were given rather than drifting by however long each callback

takes, and they drop the firings they missed when a callback overruns.

Assigning to ``timer.interval`` or ``timer.single_shot`` now updates a running

timer on every backend, and assigning the value it already holds no longer

restarts it.

`.FigureCanvasBase.start_event_loop` returns after the requested timeout

instead of after that many polling iterations. The GTK backends now run a

``GLib.MainLoop`` rather than that polling fallback.