I noticed a problem when preparing the new release. The extra entries in the bspline derivatives workspace break binary compatibility.
This isn't necessarily a huge problem, but it seems undesirable to force an upgrade of all applications just for those two struct entries. If we're going to break binary compatibility we may as well do it for all other functions that need it at the same time. So I'd propose using a separate workspace for the derivative functions in this release. See e.g. branch bspline-compat at http://src.network-theory.com/gsl.git/ which is basically finished, I just need to add some error checking.
