BUG#16393: post-review fixes: fix comments.

    ON condition of the given nested join, and does the same for nested joins 

    contained within this nested join.

  IMPLEMENTATION

  NOTES

    We can add accesses to the tables that are direct children of this nested 

    join (1), and are not inner tables w.r.t their neighbours (2).

    Example for #1 (outer brackets pair denotes nested join this function is 

    invoked for):

     ... LEFT JOIN (t1 LEFT JOIN (t2 ... ) ) ON cond

    Example for #2:

     ... LEFT JOIN (t1 LEFT JOIN t2 ) ON cond

    In examples 1-2 for condition cond, we can add 'ref' access candidates to 

    t1 only.

    Example #3:

     ... LEFT JOIN (t1, t2 JOIN t3 ON inner_cond) ON cond

     ... LEFT JOIN (t1, t2 LEFT JOIN t3 ON inner_cond) ON cond

    Here we can add 'ref' access candidates for t1 and t2, but not for t3.

*/

static void add_key_fields_for_nj(TABLE_LIST *nested_join_table,