Add test/continuous integration

[arl]

It would be quite simple to prepare a travis script that builds a Qt application, then checks that macdeployqtfix does its job.

Best thing would be to trigger the macdeployqt problem with a minimal qt command line app, so as to be able to check that it doesn't run, due to missing deps, after the macdeployqt step, but runs correctly, after the macdeployqtfix step.