inserted or removed. Refactor node insertion to not require rebalancing
all the time or a loop if it does. In rb_tree_swap_prune_and_rebalance,
don't call rb_tree_reparent_nodes, instead do the work ourselves (since
we will eventually undo half of the work of rb_tree_reparent_nodes).
functions to a separate rb_tree_ops structure. Make every int explicit
in being signed or unsigned. Use RBDEBUG to enable debug code. Move
rbt_count to RBSTATS. Use RBSMALL to not keep track of min/max.
