Octave compatibility fix: skip some tests under Octave 5.1, due to a bug in ordeig

(cherry picked from commit 9bac6a0d)

tests/stochastic_purely_forward/stochastic_purely_forward.mod

@@ -19,9 +19,15 @@ end;
 steady;
 check;
 
+% Skip test under Octave 5.1
+% ordeig() is buggy in that version (but is fixed in later ones; and in older
+% ones it is absent, so we use our replacement)
+if ~isoctave || octave_ver_less_than('5.1') || ~octave_ver_less_than('5.2')
+
 stoch_simul(periods=0, irf=30, order=1);
 stoch_simul(periods=2000, irf=30, order=1);
 
 stoch_simul(periods=0, irf=30, order=1,hp_filter=1600);
 stoch_simul(periods=2000, irf=30, order=1,hp_filter=1600);
 
+end

tests/stochastic_purely_forward/stochastic_purely_forward_with_static.mod

@@ -20,8 +20,15 @@ end;
 steady;
 check;
 
+% Skip test under Octave 5.1
+% ordeig() is buggy in that version (but is fixed in later ones; and in older
+% ones it is absent, so we use our replacement)
+if ~isoctave || octave_ver_less_than('5.1') || ~octave_ver_less_than('5.2')
+
 stoch_simul(periods=0, irf=30, order=1);
 stoch_simul(periods=2000, irf=30, order=1);
 
 stoch_simul(periods=0, irf=30, order=1,hp_filter=1600);
 stoch_simul(periods=2000, irf=30, order=1,hp_filter=1600);
+
+end