[Gretl-devel] matrix gui

It turns out the (relatively) hard work was just adapting the data editor spreadsheet for matrix use (still not as good as it could be, but workable) and hooking up a matrix back-end. That done, a lot of other things come more or less for free. So here's what we have now: * A "properties" window for matrices. Not very interesting for non-square matrices at this point, but for square ones you get a reading on symmetry, positive definiteness, determinant, eigenvalues and so on. * The gui matrix editor now has a menu of transformations such as X'X, transpose, Cholesky decomposition and such. Also a "save as" button to let you save a transformation under another name. Might be of some use for pedagogical purposes. Allin.