Unit tests in 3.0

3.0 and master now have the start of a unit test framework, in src/tests/unit/. Parts were there before, but it appears they weren't run. The build now refuses to link radiusd if the unit tests fail. More unit tests are now in src/tests/keywords/. See the README in that directory for documentation on how the tests work. We should now be able to have a large number of small tests. Each test should test one piece of the "unlang" framework. The net result should be that there are fewer regressions in functionality. Alan DeKok.