2572. [func] Simplify DLV configuration, with a new option

2572.	[func]		Simplify DLV configuration, with a new option
			"dnssec-lookaside auto;"  This is the equivalent
			of "dnssec-lookaside . trust-anchor dlv.isc.org;"
			plus setting a trusted-key for dlv.isc.org.

			Note: The trusted key is hard-coded into named,
			but is also stored in (and can be overridden
			by) $sysconfdir/bind.keys.  As the ISC DLV key
			rolls over it can be kept up to date by replacing
			the bind.keys file with a key downloaded from
			https://www.isc.org/solutions/dlv. [RT #18685]