collect-table-refs issue in sql/expressions.lisp

The sql-function-exp method collect-table-refs refers to the components slot, 
but no such slot exists - the correct slot is args.  Fix below:

(defmethod collect-table-refs ((sql sql-function-exp))
  (let ((tabs nil))
    (dolist (exp (slot-value sql 'args))
      (let ((refs (collect-table-refs exp)))
        (if refs (setf tabs (append refs tabs)))))
    (remove-duplicates tabs
                       :test (lambda (tab1 tab2)
                               (equal (slot-value tab1 'name)
                                      (slot-value tab2 'name))))))