Refactor test for Octave version

Distinguish between a minimal version required (from a source code perspective,
applicable on all platforms) and an exact version requirement (from a binary
package perspective, in practice used only for our Windows package).

matlab/dynare.m

@@ -71,13 +71,20 @@ dynareroot = dynare_config('', preprocessoroutput);
 warning_config()
 
 if isoctave
-    if octave_ver_less_than(supported_octave_version)
+    % The supported_octave_version.m file is not in git nor in the source
+    % package, it is manually added in binary packages distributed on dynare.org
+    if exist('supported_octave_version', 'file') && ~strcmp(supported_octave_version, version)
         skipline()
         warning(['This version of Octave is not supported. Consider installing ' ...
-                 'version %s+ of Octave,\notherwise m files will be used instead ' ...
-                 'of precompiled mex files and some features, like solution\n' ...
+                 'version %s of Octave\n' ...
+                 'from www.octave.org, otherwise m files will be used instead ' ...
+                 'of precompiled mex files and some\nfeatures, like solution ' ...
                  'of models approximated at third order, will not be available.'], supported_octave_version())
         skipline()
+    elseif octave_ver_less_than('4.2') % Should match the test in mex/build/octave/configure.ac
+        skipline()
+        warning(['This version of Dynare has only been tested on Octave 4.2 and above. Dynare may fail to run or give unexpected result. Consider upgrading your version of Octave.'])
+        skipline()
     end
 else
     if matlab_ver_less_than('7.5')

matlab/supported_octave_version.m

-function v = supported_octave_version()
-
-% Copyright (C) 2017 Dynare Team
-%
-% This file is part of Dynare.
-%
-% Dynare is free software: you can redistribute it and/or modify
-% it under the terms of the GNU General Public License as published by
-% the Free Software Foundation, either version 3 of the License, or
-% (at your option) any later version.
-%
-% Dynare is distributed in the hope that it will be useful,
-% but WITHOUT ANY WARRANTY; without even the implied warranty of
-% MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-% GNU General Public License for more details.
-%
-% You should have received a copy of the GNU General Public License
-% along with Dynare.  If not, see <http://www.gnu.org/licenses/>.
-
-v = '4.2.1';
\ No newline at end of file