Fix iallgather problem with intercommunicators

A problem was found with the libnbc MPI_Iallgather
routine when using intercommunicators.  Special
thanks to Takahiro Kawashima(Fujitsu) for the patch
and a test case.  Verified master fails without the
patch and the test passes with the patch applied.

open-mpi/ompi@bb65835816056b1f51d6b91ee3998f836634e9bc