This reverts commit a080f3ca.

increased offset for dirichlet in case things go wrong, makes things less extreme and less prone to breaking

fixing bug in resampling.  needed to compute scaled statistics using the precisions.  as an added benefit, this avoids memory copies, and should make the code a bit faster.

adding a robust regression class with multivariate-t distributed noise.  no sampling of degrees of freedom yet.

ensure nu is int when sampling inverse wishart