The MPI Standard specifies a mechanism for installing one's own error handler,
and specifies the behavior of two predefined ones, MPI_ERRORS_RETURN
and MPI_ERRORS_ARE_FATAL.
As part of the mpe library, we include two other error handlers to
facilitate the use of dbx in debugging MPI programs.
MPE_Errors_call_dbx_in_xterm
MPE_Signals_call_debugger
These error handlers are located in the mpe directory.
A configure option (-mpedbg) includes these error handlers into
the regular MPI libraries, and allows the command-line argument
-mpedbg to make MPE_Errors_call_dbx_in_xterm the default
error handler (instead of MPI_ERRORS_ARE_FATAL).