Bago dti min

There are too many commits here, but some of these should go away when you rebase your branch on master. It's the recent merge of the LiFE branch.

The last commit is what I am proposing. How about that? I have set it so that a voxel with 0 signal is considered to be masked (there's something wrong with that one anyway, no?) and a signal with a very low signal has high eigen-values. What do you think? Does this solve your issue? Any other ideas?