Exercise 3.48: Explain in detail why the
deadlock-avoidance method described above, (i.e., the accounts are numbered,
and each process attempts to acquire the smaller-numbered account first) avoids
deadlock in the exchange problem.  Rewrite serialized-exchange to
incorporate this idea.  (You will also need to modify make-account so
that each account is created with a number, which can be accessed by sending an
appropriate message.)