Without this, they can activate after any call to the event processing,
so they may activate in cases such as when updating progressbar while
loading a document, or on repeated user input (so things like showing
spellchecking get updated when the app is busy redrawing). This change
makes idle timers activate only when there's nothing more for the event
loop to process. It's a bit of a question if this doesn't break something
that happens to expect idle timers to be not-really-idle timers, but oh well.

No change for non-X11 platforms, as there's I don't know how to check
the event queues.

Change-Id: I074a88f2f5eeb4b456a11916a0ec2ad6f54dfbab