Partial fix for bug #7224 (https://gna.org/bugs/?7224).
The 'param_types' argument of the 'diffusion_tensor.init()' user function was changed to the value
of 3. The rational for this fix is given in the post at
https://mail.gna.org/public/relax-devel/2006-09/msg00042.html (Message-id:
<7f080ed10609300034j2e2487f2p2e252eb941a38e33@...>).
