In 98bdf76581, all XLSX files were removed in
favour of XLS, for compatibility with MATLAB R2009b.
But this broke the very same tests under Octave, since XLS support is not very
good there.
This commit implements a solution that works everywhere, by using XLSX whenever
possible, and XLS otherwise.
— use XLS instead of XLSX in testsuite datafiles
— use optimset instead of optimoptions
— use quadv/quadl/quadgk instead of integral
— fix race condition in load_m_file_data_legacy.m tests
— use fallback implementation for intersect(…, 'stable')
Johannes Pfeifer
Sébastien Villemot
Stéphane Adjemian (Charybdis)