spdiags.m: Treat sub/super-diagonals the same as Matlab. Distinguish between M >= N and M < N cases when placing diagonals. * spdiags.m: Add test for M >= N or M < N. When M >= N, sub-diagonals are taken from the first entries in a column while super-diagonals are taken from the last entries in a column. This is reversed for M < N. Add %!tests for new behavior. Add seealso link to diag() in docstring.

gnulib-hg = gnulib-hg