window minimised and unminimised signals

[Tim Cuthbertson <tim gfxmonk net>]

Are there any signals for these events in gnome-shell?

Right now I've managed to infer these events when the window's actor
'size-changed' signal fires, using the following logic:
 - if the window's `minimised` property is now true, assume the window
has just been minimised,
 - if the current value of global.screen.get_display().get_grab_op()
== Meta.GrabOp.COMPOSITOR, then it seems to be an un-minimize event.

Those are pretty hacky, and the latter in particular is downright
guesswork. Is there a better way?

Cheers,
 - Tim.