OpenMPI 1.8.6 memory leak warning

[Ondrej Marsalek]

Dear CP2K users,

there is a memory leak in OpenMPI 1.8.6 that makes CP2K 2.6 grow in
memory utilization quite fast - more so with diagonalization than OT.
It happens in MPI parallel runs, even with only shared memory
communication within one node. Switching to the just released OpenMPI
1.8.7, which lists a plugged memory leak in blocking sends in its list
of changes, fixes the problem. Perhaps this warning will save somebody
some headache.

Best regards,
Ondrej