Most subsystems are now created via the subsystem manager using the global
subsystem registrations.
The FGGlobals add_subsystem() and add_new_subsystem() methods have been removed
as the subsystem manager addition and creation function interface now exceeds
the functionality of these helper functions.
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.
