Add documentation to TestSystem interface.
Let SlimCommandRunningClient throw IOException in case of a connection problem.
Avoid throwing null-pointers when close() is called on SuiteHistoryFormatter.
Ensure testSystemStopped event is sent when an IO error occurs in FitTestSystem.
Ensure testSystemStopped event is sent when an IO error occurs in SlimTestSystem.
Merge pull request #350 from amolenaar/fix/350

no logfile on aborting test execution