Improve test system to avoid use of old jar or jar from other branch

[nsoft]

In the current test infrastructure, the build builds several small unojars and then executes them to verify that the correct results are printed, however there is a risk that without a clean, old versions of the jar are retained, or that the build decides that they are up-to-date especially when switching branches.

We should enhance the build to add the commit hash to the jar file as a manifest attribute and the test classes to accept the commit hash as an argument or perhaps system property, and then as a standard prat of the test infrastructure for the jar invoked has the same commit hash as the checkout in which the tests are running.