* Some platforms do not use the POSIX exit code, but at least have the
  decency to give a textual report we can use in the test framework.
* Some totally fail to report this on their own. For those systems a
  work-around was implemented.

* Also ensure that defective installations are diagnosed when possible,
  even when the user does not care.

* On some compilers it's a struct and cannot be used in arithmetic
  expressions.

* Pass --with-on-demand-check-programs to configure to only build
  test programs when make check is invoked.

* Some compilers deliver this Fortran 2008 feature which hopefully saves
  a function call.

* Use fast arithmetic if overflow cannot happen.
* Fallback on long arithmetic for large intermediate values when needed.

* Older versions of automake would create files named '#' or
  'am--include-marker' without this edit.

* Some MPI implementations annotate INTENT(IN) parameters with
  const, some do not.

* gfortran warns when using mpi_address_kind directly. Therefore using
  the corresponding kind from iso_c_binding removes those warnings.

* This way problems with floating-point comparisons are avoided.