Rework the default loader into a cleaner, more explicit FallbackLoader, and turn the previously chained loaders into ingredients that could be used in this or other loaders.
Various fixes from review, including style fixes for square's codebase, typos, clean up some extra logging, etc.
Merge pull request #279 from cgruber/speeduploader

Rework the default loader into a cleaner, more explicit FallbackLoader