emit focus_lost event, add events.FOCUS_LOST

[brainrake]

Expose focus_lost event to lua. A handler was already registered in gtk, so this is a small change.
This change enables autosave on focus lost, a convenient, previously requested feature.

[orbitalquark]

With your patch, this event will not be emitted when the command entry is active and the window loses focus. Also, the event will be emitted if the command entry loses focus, but the window remains in focus. You might try if (widget == window) emit(lua, "focus_lost", -1); on the first line of the function. I'll experiment with it too.

[brainrake]

Thanks, I wasn't sure about the order.
Seems to be working fine. There is one possible quirk: focus lost event is emitted when dialogs are opened (save, command chooser, etc). I find this behavior acceptable, just wanted to note it.

[orbitalquark]

Not only that, but the event is emitted twice for me. I'm not sure if this is a GTK issue or not. I would rather have the event emitted only once.

[orbitalquark]

After more investigation, I think it's my window manager. Alt-Tabbing away from Textadept emits 2 focus lost events, but clicking away only emits one. I'll clean up this patch a bit and commit something similar. Thanks!

[orbitalquark]

Closed via 4d661eb `events.UNFOCUS` is the event name in order to complement the existing `events.FOCUS`.

[brainrake]

Cheers!