[scikits-image] Restore previous io plugins (#152)

[James Turner]

> Ideally, the ``imread(..., plugin='fits')`` functionality should
> auto-load the FITS-plugin---I should see why this is not currently
> working, because it seems like a bug.

Oh, did someone say FITS plugin? I've been meaning to get back to
that (sorry, too busy trying to finish up our Python distribution
for astronomy). I believe I had some uncommitted changes after SciPy
that we were pending me figuring out how to deal with metadata.

I can try to look at this but it might take a couple of days to get
to. Please let me know if you have Qs in the meantime (I'm not sure
about auto-loading off the top of my head).

Cheers,

James.