dns/rbt.h; it was needed only by compress.c and zt.c.

                        and dns_rbt_deletenode was added.

deletion no long requires a valid chain.  chain gook removed from all
of the deletion functions.

Minor unrelated doc & code convention cleanups.

Prototyped and documented dns_rbt_deletenode.

negatively cached.

Remove this check from the validator, and remove more redundant constants
from dst.h

being changed.
Fix typo.

isc_task_mem() has been eliminated.
Use memory context reference counting.

Timers now use the timer manager's mctx, not the task's.

isc_mem_setsplit().  Rename isc_mem_destroy_check() to
isc_mem_setdestroycheck().  Add isc_mem_inuse().

handler actually work in the easy case.