[v9_9] limit recursion depth and iterative queries

[v9_9] limit recursion depth and iterative queries

4006.	[security]	A flaw in delegation handling could be exploited
			to put named into an infinite loop.  This has
			been addressed by placing limits on the number
			of levels of recursion named will allow (default 7),
			and the number of iterative queries that it will
			send (default 50) before terminating a recursive
			query (CVE-2014-8500).

			The recursion depth limit is configured via the
			"max-recursion-depth" option.  [RT #35780]