Fix testsuite for Octave

On master, some mod files do not yet run with Octave due to e.g. missing functions and other small bugs. Here is an (updated) list, when I push fixes I'll update the list:

• analytic_derivatives/BrockMirman_PertParamsDerivs (on RHEL/CentOS, but not Fedora, with KRONFLAG=-1)
• estimation/method_of_moments/* (use nanmean instead of mean(x,'omitnan'; randstream not implemented in Octave;maybe other errors)
• bgp/* (many problems, probably numerical imprecision, also due to incompatibilities from and differences in toolboxes such as optim)