RFC/coll basic neighbor

Following the discussion started on the devel mailing list at http://www.open-mpi.org/community/lists/devel/2014/08/15713.php
i reverted r32796 / 9c788ff9400960823637dc0eebb3a8640414fa05 and applied the patch i posted to the mailing list.

@hjelmn could you please review this before it gets merged into the master ?