Adds a static method for getting the label of a Node.  Improves the way Partial
applications are printed.  E.g.:

    TRACE> (indexp (map head<0> (iterate the_filter<0> (iterate suCC<0> 2))) 1)

Running on yellow-eyed.
------ Config refcnt-opt ------
reverse              0:01.05
tak                  0:00.64
rfib                 0:00.15
exp3_8               0:00.21
tree_insert          0:00.45
tree_insert_32       0:00.43
------ Config gc-opt ------
reverse              0:00.69
tak                  0:00.61
rfib                 0:00.11
exp3_8               0:00.10
tree_insert          0:00.52
tree_insert_32       0:00.53