Find way to activate long testing in Travis easily

[jni]

Some tests were taking too long, so I replaced them with corresponding tests with tiny data. Nevertheless, the long tests are still there with a skipif decorator (see here) and they are useful to run occasionally because they use real data. It would be great to enable them easily on Travis e.g. with a flag in the commit message, e.g. for refactors that alter large chunks of code. I haven't yet explored how this can be done realistically.

[jni]

The naive way to do this would be with a commented-out line in .travis.yml that sets the corresponding environment variable. But it's not very elegant at all to litter the git history with commits commenting and uncommenting this one line.

[jni]

Another option: have the travis script grep the latest commit message for a specific message, and set the flag if it is there.