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make sure it doesn't go to sleep on me! had to also turn off the screen saver.
Randomly re-named by typing without looking, then removing non-alpha characters.
Just after I took this screenshot, I clicked a picture and the preview pane slid in from the right. D'oh!
one step backward, rerandomizing.
now choosing some pix, note the upper left, where the button is set to the list view instead of preview.
Huzzah!