Exercise 3.4.  Modify the make-account procedure of exercise 3.3  by 
adding another local state variable so that, if an account is accessed 
more than seven consecutive times with an incorrect password, it invokes 
the procedure call-the-cops.

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(define (make-account balance password)
  (define bad-password-count 0)
  (define (withdraw amount)
    (if (>= balance amount)
        (begin (set! balance (- balance amount))
               balance)
        "Insufficient funds"))
  (define (deposit amount)
    (set! balance (+ balance amount))
    balance)
  (define (dispatch p m)
    (cond ((not (eq? p password))
             (set! bad-password-count (+ bad-password-count 1))
             (if (> bad-password-count 7)
                 (call-the-cops)
                 "Incorrect password"))
          ((eq? m 'withdraw) withdraw)
          ((eq? m 'deposit) deposit)
          (else (error "Unknown request -- MAKE-ACCOUNT"
                       m))))
  dispatch)