uber/image-diff — pull request #3 by twolfson (2014-02-05 02:30:06+00:00)
Title: Fixing up regressions on machines sans graphicsmagick

While attempting to use `image-diff` on a Vagrant box, I ran into false positives of tests passing when I lacked `graphicsmagick` entirely. This PR fixes that.

I decided to not write a regression test against this since it complicates the `.travis.yml` significantly.

/cc @mlmorg