Due to MPI_Comm_idup we can no longer use the communicator's CID as
the fortran handle. Use a seperate opal_pointer_array to keep track of
the fortran handles of communicators.

This commit also fixes a bug in ompi_comm_idup where the newcomm was not
set until after the operation completed.

cmr=v1.7.4:reviewer=jsquyres:ticket=#3796
Fix typo in communicator destruction