Match different colorspace output from different versions of ImageMagick

Fixing ImageMagick 6.6/6.7 -> 6.8 incompatabilities

Fixing inversion

Fixing regex check

Added test for pre 6.8 version (with file)

Making sure that shelling out works

Changing the test that reads from a buffer

Reverting changes to the pre/post-images that was a part of the workaround between ImageMagick releases

Don't try to read from a StreamIO object without a path

Fixes the strange issue where we tried to read from a StringIO-object

Reverting old change where I changed buffer to a String