Fix for: https://sourceforge.net/p/flightgear/codetickets/2059/
When copying addon-config into the main property tree, skip props
which already exist and which are marked ARCHIVE, on the assumption
they came from autosave.xml.
This includes the basic CMake infrastructure for building and executing the test
suite. Four test categories have been added - unit, system/functional, GUI, and
simgear unit tests. The test suite is run by typing 'make test_suite'.
All of the fgfs sources are included in the new run_test_suite executable,
excluding the bootstrap routine and its main() function. The test suite
currently consists of a single dummy unit test for the NasalSys subsystem, and a
single demonstration simgear/props unit test.
