Sort on filenames, not random bits of memory.
Reenter the loop at the top.  This fixes decks with no cover slide.
Add a -b <background-color> option to specify a background color and
prevent the bleeding of images to the edge of the screen.

This change probably looks a bit odd with composited slides.  This will
be addressed when we're back to having a working sandbox.
Add a -w option to set the initial resolution.

Useful for tablest configured specficaly for HDMI presentations.
Add a fb_progress_bar function.
Add a busy indicator and progress bar when precaching images rather than
spamming the scren with them.