Smooth previews for open/save dialogs

[John Tapsell]

Rafael,
  Hey, it's looking nicer :)

Things I noticed:

* When you change folders, the preview no longer disappears like it
did in the first example that you showed us.  I'm guessing this is a
bug?
* To me it seems to flicker..  which I don't really like :/

  I don't really get why you guys didn't like my first idea:
When there is no existing preview, have a nice long fade in.
When there is a preview, have no fade etc.

  This way you can even send the 0.4s on a nice fade in, and it won't
be annoying because you'll only see it once per folder change

It's all subjective :)

John