Add --dnssec-timestamp option and facility.

man/dnsmasq.8

@@ -674,6 +674,12 @@ that dnsmasq should be started with this flag when the platform determines that
 reliable time is established, a SIGHUP should be sent to dnsmasq, which enables time checking, and purges the cache of DNS records
 which have not been throughly checked.
 .TP
+.B --dnssec-timestamp=<path>
+Enables an alternative way of checking the validity of the system time for DNSSEC (see --dnssec-no-timecheck). In this case, the 
+system time is considered to be valid once it becomes later than the timestamp on the specified file. The file is created and 
+its timestamp set automatically by dnsmasq. The file must be stored on a persistent filesystem, so that it and its mtime are carried 
+over system restarts. 
+.TP
 .B --proxy-dnssec
 Copy the DNSSEC Authenticated Data bit from upstream servers to downstream clients and cache it.  This is an 
 alternative to having dnsmasq validate DNSSEC, but it depends on the security of the network between