MPI_Type_indexed.3in: fix array_of_displacements type

This man page contains the prototype and descriptions for both
MPI_TYPE_INDEXED and MPI_TYPE_CREATE_HINDEXED.  Bastian Beischer
noticed that the type of the array_of_displacements argument in the
MPI_TYPE_CREATE_HINDEXED was wrong.

Also, a minor update to MPI_Type_hindexed.3in: indicate that the C
type is MPI_Aint and the Fortran type is INTEGER (which is why this
function was deprecated and then deleted by the MPI Forum!).

cmr=v1.8.1:reviewer=dgoodell