Yet another batch of Octave compatibility fixes

matlab/ols/pooled_ols.m

matlab/ols/sur.m

tests/ecb/SUR/panel_var_diff_NB_simulation_test.mod

tests/ecb/SUR/panel_var_diff_NB_simulation_zero_eq.mod

tests/ecb/SUR/sur_noniterative.mod

tests/ecb/SUR/sur_params_noniterative.mod

tests/ecb/pooled_fgls/panel_var_diff_NB_simulation_test.mod

tests/ecb/pooled_fgls/test_param_names.mod

tests/ecb/pooled_ols/panel_var_diff_NB_simulation_test.mod

tests/ecb/pooled_ols/test_param_names.mod

tests/estimation/univariate/ols/mc-ols.inc

tests/histval_initval_file_unit_tests.m