* libtool does not pass -shared-intel through the link step even though
  it is very much needed for linking to libraries built with older versions
  of the Intel compiler.

* xt_quicksort_base.h is included to generate quicksort functions.

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

* Where only part of a condition (#if) is known, this change enables
  substitution of those parts.

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

* While it would be desirable to have buffer declared const when the
  underlying MPI allows const buffer parameters to MPI_Unpack,
  that is not guaranteed to work so we keep the parameter declared void *
  instead of const void *.

* gfortran warns about passing variables to C when not using a type kind
  known to be interoperable.

* This prevents overflows later on, however theoretical.

* This also permits the conversion to restrict in a manner
  conforming to the language rules.

* This way the test code is clearer and the initialization can be
  easily re-used.

* By always dividing 2*j by 2*j when j > 0 or 1 if j == 0.

* buffer is already of type unsigned char *.

* xt_int_kind was moved to xt_core.

* This way no casting is needed at the call-site.

* This simplifies the caller.

* The warning is generated when -Winteger-truncation is enabled.