[gthumb-list] Some race conditions

[Ryan Rowe <ryanrowe zoho com>]

I think I've found a few race conditions:

1. If you click the rotate left/right button fast enough, the thumbnail gets out of sync with the photo, and the photo sometimes gets out of sync with what is on disk

2. If you label a photo (say with "2") then switch to the view for "2", and delete that photo, it will still show in the main view when you go back.

3. If you delete a photo in the "2" view, and go back to the other main view, the thumbnails get out of sync with the photos, meaning you can delete photos you didn't want to.

4. Same for deleting a photo outside of gthumb.