Added a test (AIC model selection between diffusion tensors) to the relax test-suite.
This test triggers the problem reported by Chris MacRaild at
https://mail.gna.org/public/relax-devel/2006-04/msg00020.html. The test has been added to aid in
the removal of bug #5746 located at https://gna.org/bugs/?func=detailitem&item_id=5746.
