Imagemagick doesn't respect input colorspace

Turns out Issue 25 was a bit more insidious. There may still be some input problems when scaling sRGB or other nonlinear inputs, but the real problem is that IM doesn't AUTOMATICALLY set the output image's colorspace correctly (or even take it as any kind of useful hint.) It presupposes everything should be sRGB, always, forever.

So this settles that. There is the distinct possibility that IM does this for every transformation which results in a new image, but more testing is needed.

BTW I did bother to run the tests before submitting the patch this time. Whoops!