Some implementations have issues with using MPI_BOTTOM in MPI_Bcast.
If that the case we can use an alternate implementation.
There is a macro in config.hpp named BOOST_MPI_BCAST_BOTTOM_WORKS_FINE
that can be used to control that. broadcast_test.cpp print a message
that point to that macro if suspicious behavior is detected.
LAM and Bull X MPI seems to have that problem.
