Recursively compare the branches of a node in nodes-equalp.

This was causing some of the lift tests to fail.

## Before
    BTRIE-TESTS> (run-tests :suite 'btrie-tests)
    Start: BTRIE-TESTS
    Start: BTRIE-LOOKUP
    Start: TEST-OBTAIN-SEQ
    Start: BTRIE-PREDICATES
    Start: TEST-NODES-EQUALP
    Start: TEST-INIT
    #<Results for BTRIE-TESTS 4 Tests, 3 Failures>

    BTRIE-TESTS> (describe *)
    Test Report for BTRIE-TESTS: 4 tests run, 3 Failures.
    
    Failure: test-obtain-seq : simple-lookup
    
      Condition    : Ensure-same: (a 1 .) is not NODES-EQUALP to (a 1 .)
      During       : END-TEST
      Code         : 
      ((LET ((TR (MAKE-TRIE *BANANA*)))
         (WITH-SLOTS ((K KEY) (W WIDTH) (B BRANCHES))
             (LET ((RESULT-NODE))
               (ENSURE-SAME (OBTAIN-SEQ TR "banana")
                            (MAKE-NODE :KEY #\a :WIDTH 1 :BRANCHES
                                       (LIST (MAKE-LEAF)))
                            :TEST #'NODES-EQUALP)))))
      
    Failure: test-nodes-equalp : leaf-nodes
      
      Condition    : Ensure-same: (. 1 is not equal to (. 1
      During       : END-TEST
      Code         : 
      ((ENSURE-SAME #1=(MAKE-LEAF) #1#))
      
    Failure: test-nodes-equalp : empty-tries
      
      Condition    : Ensure-same: ("" 0 is not equal to ("" 0
      During       : END-TEST
      Code         : 
      ((ENSURE-SAME #1=(MAKE-TRIE) #1#))
      
    Test Report for BTRIE-TESTS: 4 tests run, 3 Failures.
    ; No value

## After
    BTRIE-TESTS> (run-tests :suite 'btrie-tests)
    Start: BTRIE-TESTS
    Start: BTRIE-LOOKUP
    Start: TEST-OBTAIN-SEQ
    Start: BTRIE-PREDICATES
    Start: TEST-NODES-EQUALP
    Start: TEST-INIT
    #<Results for BTRIE-TESTS [4 Successful tests]>