Continuous integration improvements

Further to undetected failures in tests after some past commits, I've decided to propose some improvements related to continuous integration:

- Test against all available backend versions in travis (9.1, 9.2, 9.3)
- Make ant fail if any test fails to ensure travis won't see a false success
- Make travis run tests for junit 4 and 4.1 whenever applicable (I removed the check for junit availability in ant classpath as we now have a maven dependency for that)

I've fixed remaining tests that were previously failing in travis environment.