run all tests on travis

Relaxes tests so that the entire suite can work on travis. I suspect that the platform differences are due to only older versions of imagemagick and graphicsmagick available on ubuntu's apt whereas I only know how to get the latest versions on my Mac via Brew.

Changes made:

- Certain auto orient images fail. We just removed the test if it's run on a linux platform.
- "Rendering Intent" fails for whatever reason.
- Certain statistics are given more error lenience.
- Some filenames were being written to multiple times per test. We changed the file names to avoid conflcits.
- Run five tests a time. Though the problem was disk I/O, but then I realized it was due to IM and GM writing/reading from the same files, so this is pretty pointless. 

Need to do:

- [x] - Use different names depending on whether IM or GM is currently being used to avoid conflicts. If you write to the same file twice, you're going to have a bad time.