Smooth previews for open/save dialogs

[Rafael Fernández López]

Hi,

> ok, *this* i like very much. for me, it addresses both the "to grey
> flicker" 
> and the speed issues the previous version had. i think this would be very

> cool for 4.0 ...

Hehe, well I still need to polish some minor stuff, but it is almost
finished... (John noticed a small bug I was aware of :P)

> and yes, previews right in the icon view would be great and should be
> added at 
> some point (note, however, that this can really slow down the dialog 
> undesirably, so personally i'd still like us to keep the preview pane.)

Well, the preview pane is on the menu, and I really think it should stay
there forever, without taking in count if we add a view for previews.