Efficiency change. OCTAVE_VERSION is a builtin function in Octave.

(cherry picked from commit 59739c38)

src/initialize_dseries_class.m

@@ -62,7 +62,7 @@ if ~exist('ndim','file')
     p{end+1} = 'utilities/missing/ndim';
 end
 
-if ~exist('OCTAVE_VERSION') && isstandalone
+if ~exist('OCTAVE_VERSION', 'builtin') && isstandalone
     p{end+1} = 'utilities/missing/dims';
 end
 
@@ -74,7 +74,7 @@ if ~exist('get_file_extension','file')
     p{end+1} = 'utilities/missing/get_file_extension';
 end
 
-if exist('OCTAVE_VERSION') && ~exist('user_has_octave_forge_package','file')
+if exist('OCTAVE_VERSION', 'builtin') && ~exist('user_has_octave_forge_package','file')
     p{end+1} = 'utilities/missing/user_has_octave_forge_package';
 end
 
@@ -90,23 +90,23 @@ if ~exist('one_sided_hp_filter','file')
     p{end+1} = 'utilities/missing/one_sided_hp_filter';
 end
 
-if ~exist('OCTAVE_VERSION') && ~exist('ismatrix','builtin')
+if ~exist('OCTAVE_VERSION', 'builtin') && ~exist('ismatrix','builtin')
     p{end+1} = 'utilities/missing/ismatrix';
 end
 
-if ~exist('OCTAVE_VERSION') && ~exist('isrow','builtin')
+if ~exist('OCTAVE_VERSION', 'builtin') && ~exist('isrow','builtin')
     p{end+1} = 'utilities/missing/isrow';
 end
 
-if ~exist('OCTAVE_VERSION') && ~exist('iscolumn','builtin')
+if ~exist('OCTAVE_VERSION', 'builtin') && ~exist('iscolumn','builtin')
     p{end+1} = 'utilities/missing/iscolumn';
 end
 
-if ~exist('OCTAVE_VERSION') && ~exist('strsplit','file')
+if ~exist('OCTAVE_VERSION', 'builtin') && ~exist('strsplit','file')
     p{end+1} = 'utilities/missing/strsplit';
 end
 
-if ~exist('OCTAVE_VERSION') && ~exist('strjoin','file')
+if ~exist('OCTAVE_VERSION', 'builtin') && ~exist('strjoin','file')
     p{end+1} = 'utilities/missing/strjoin';
 end