restore ability to load fog from source without bundler

from discussion on e5c438a20661d7d71b5e583edf7cbadabab6d43b (@krames @geemus)

This should restore the ability to load fog from source without bundler. It does not add support for requiring individual fog providers by source without bundler, since that would require adding this load path hack to each provider's file. Let me know if I should do that?