Modify the output master to accept three types of messages from the slaves.
These types are
<UL>
<LI>Ordered output (just like the previous exercise)
<LI>Unordered output (as if each slave printed directly)
<LI>Exit notification (see below)
</UL>
The master continues to receive messages until it has received an exit message
from each slave.  For simplicity in programming, have each slave send the
messages
<PRE>
<CODE>
Hello from slave 3
Goodbye from slave 3
</CODE>
</PRE>
with the ordered output mode, and
<PRE>
<CODE>
I'm exiting (3)
</CODE>
</PRE>
with the unordered output mode.
