Ref. #1713
— 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')
Also added tests to check that we are able to identify the Balanced Growth Path, note that it does not work with tests/bgp/fs2000.mod.