dns_rbt_node_t changed to dns_rbtnode_t to match ISC conventions.

  main() test routine and support functions removed, to be put in
    bin/tests/rbt_test.c

  adding a node and rotating left/right taught to not use parent pointers.

  deletion disabled because it currently does not know how to not use
    parent pointers, and since they are not being maintained by insertion,
    deleting has no prayer of working.

  several isc_result_t returns changed to dns_result_t.