Add test suite

[fingolfin]

A test suite (which also tests the various error handling bits) would be nice. One way to do that: Add a separate repository ReleaseToolsTest. In there, have a branch containing a "fixed" initial state, with a fake package. The test scripts reset the master branch and tags to that (or other) git revisions (and also delete / create releases via the GitHub APIs etc.). They can then simulate various situations, and test how the script reacts to them

[fingolfin]

Just realized that testing for uncommitted changes had been broken for 1.5 years. ARGH! A test suite is really needed. Perhaps also a rewrite to make it easier? I.e. so that individual "functions" can be tested on their own?

The test suite should ideally test ever single error in the script.