Use random file name inside test for load_m_file_data.m

For unknown some reason, this fixes the test under Octave when run from the
whole testsuite.

src/read/load_m_file_data.m

@@ -55,7 +55,8 @@ return
 
 %@test:1
  % Create a data m-file
- fid = fopen('data_m_file.m','w');
+ datafile = [tempname '.m'];
+ fid = fopen(datafile,'w');
  fprintf(fid,'FREQ__ = 4;');
  fprintf(fid,'INIT__ = ''1938Q4'';');
  fprintf(fid,'NAMES__ = {''azert'';''yuiop''};');
@@ -71,9 +72,8 @@ return
 
  % Try to read the data m-file
  try
-     datafile = 'data_m_file.m';
      [freq, init, data, varlist, tex, ops, tags] = load_m_file_data(datafile);
-     delete('data_m_file.m');
+     delete(datafile);
      t(1) = 1;
  catch exception
      t(1) = 0;