1.  Clean up mpinu library.
2.  Better diagnostics by MPINU if:   rsh host gapmpi
      fails.  Should mention procgroup file in error message.
3.  Should hook -p4pg command line into gapmpi.sh;  Does it hurt slave side?
       Arrange for mpinu to work with ./gapmpi.sh on command line.
      e.g.:  gapmpi.sh -p4pg pkg/gapmpi/bin/procgroup
        and remote ./gapmpi.sh will come from pkg/gapmpi/bin/./gapmpi.sh
        but should really start up in $PWD ??
      One idea is to add:   PROCGROUP=-p4pg ...     to gapmpi.sh
        and then use it on command line for gapmpi, if it doesn't
	interfere with slave.
4.  Write an INTERNALS document.
5.  Maybe a SendRecvMsg() should flush old messages from that source first.
6.  SendMsg("Print(3+4)");
      Should print immediately, and not wait for newline.
      See why that stopped working.
6.  Can lib/{masslave,slavelist}.g be run from pkg/gapmpi/lib/ ?
    Can they be invoked at startup by pkg/gapmpi/{read,init}.g ?
7.  USE:  LastReadValueGVar for GAPMPI_Last(), now that LastReadValueGVar has
     been added to src/streams.c:READ() in GAP-4.x
