Simple script to install libraries this project depends on; a naive
way of bootstrapping this onto new machines.
Handle JPG and PNG directly with PIL, and pipe all other files through
dcraw (assuming it's on the path). Also, add exception handling enough
that we nicely ignore files that either dcraw or PIL refuse to load.

This is enough that I can process a directory containing .jpg, .xmp
and .nef files (and we create thumbnails for the .jpg and .nef and
ignore the .xmp).