only be used if the RTE init functions have been called. Not quite as
flexible as the real waitpid() function (no -1 support), but all I need
for the SSH / BProc / RMS pcms. This code is not yet turned on by
default (need to add the init / finalize calls to ompi_rte_init?? and
ompi_rte_finalize()
This commit was SVN r2860.