Updates to the testing system.  
* New tests, and a way to test them.
* CMakeLists files updated to include new files, and to reference both .cpp and .h files, so they can be part of the project and therefore searchable.
* Add a way to point to the test files directory.
* Split FBC tests into their own test.
* Add commented-out way of outputting raw data for the sbml.org online validator.
* Better comments for various tests.
* Make test model reactions reversible (since they are).