Fix reorientation of images for magick [#16]

Magick's rotate arguments go the other direction from PIL's, so
reorient_image was turning portrait images upside-down! I should've
tested 3c61cbc57d0fd31673c166bd84826039c7a62503 more thoroughly.
Don't specify a filter to ImageMagick [#16]

I thought it would need instructions because PIL did, but it seems
perfectly capable of figuring out a wise algorithm on its own.
 Merge branch 'magick-fixes' into 'version-5'

Closes #16