Update .travis.yml

This *might* fix it enough for all tests to run (maybe?)
Update .travis.yml

Doh, the shebang line for run-tests itself relies on `python3`
Update .travis.yml

Add diffing of failure logs
Update .travis.yml

Seems like I'd inadvertently created invalid YAML!
Merge pull request #486 from lurch/patch-1

Update .travis.yml to use python3.3