It solve the problem with the MPI_Aint alignment that showed up on Solaris
Sparc and on heterogeneous environments when dealing with the data-type description.
The solution is to move the displacement array from the packed array if we
detect that the local architecture required MPI_Aint to be aligned to an
MPI_Aint boundary (which is not the case for x86 architectures if MPI_Aint
is a 64 bits type).
This commit was SVN r15395.