— On GNU/Linux, the locally installed binary now has priority over the
  system-wide binary
— Do not require 32-bit binary if we are on a 64-bit system and the 64-bit
  binary is there (or vice versa)
— Code factorization in the detection logic

Closes: #41

On Windows and macOS, those binaries are now bundled in packages. On Debian,
one can use the official x13as package.

All issues are now fixed, and we want to detect regressions early.

Also shorten test names, because “testsuite_old_matlab” is too long and gets
truncated on the web interface.

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

Previously, .mdl files would unnecessarily be passed through importdata(),
which crashes on Octave.

The nested “if”s (testing for the output file extension) have been reorganized,
so that importdata() is not called on .mdl files (and neither on .acm and .rcm,
where is not needed either).

@rdivide is actually more correct, because we’re not doing an
element-by-element division.

And, more importantly, MATLAB R2009b does not accept @mrdivide in bsxfun.

Provide alternative implementations, taken from Dynare.

prod() does not accept logical arrays, need to explicitly convert to doubles.

MATLAB R2009b is not able to handle HTTPS requests.

Also, having the data in the git makes the testsuite robust to network failures.

Provide alternative implementations, taken from Dynare.

addpath does not deal well with relative path on older MATLABs.

for dseries (see 48115cb8, which does not work with Octave) or a
method (see ef923e41, which does not work with all supported Matlab's
versions) to initialize the dseries class.

Fixed dependency on m-unit-tests toolbox.

Takes into account the change for the dseries initialization routine.

To initialize the toolbox:

 - Add the `src` folder in the path
 - run `dseries().initialize()`

This is an Octave compatibily workaround, Octrave cannot handle
simultaneously +folder (namespace) and @folder (class).

Using the old HTTP URL makes test fail.