Allow the trunk to cimpile after r29265. The addition of the neighborhood
collective to the mca_coll_base_comm_coll_t structure increased the size
of the ompi_communicator_t over the limit of the predefined padding
(PREDEFINED_COMMUNICATOR_PAD).

This fix is a temporary fix to allow the trunk to compile. Unfortuantely
it breaks the compatibility with all other versions of Open MPI. Please
read the comment in this header file for a more complete explanation.