Improve efficiency of DNSSEC.

The sharing point for DNSSEC RR data used to be when it entered the
cache, having been validated. After that queries requiring the KEY or
DS records would share the cached values. There is a common case in
dual-stack hosts that queries for A and AAAA records for the same
domain are made simultaneously.  If required keys were not in the
cache, this would result in two requests being sent upstream for the
same key data (and all the subsequent chain-of-trust queries.) Now we
combine these requests and elide the duplicates, resulting in fewer
queries upstream and better performance. To keep a better handle on
what's going on, the "extra" logging mode has been modified to
associate queries and answers for DNSSEC queries in the same way as
ordinary queries. The requesting address and port have been removed
from DNSSEC logging lines, since this is no longer strictly defined.

src/dnsmasq.h

@@ -690,7 +690,6 @@ struct hostsfile {
 #define STAT_SECURE_WILDCARD    7
 #define STAT_OK                 8
 #define STAT_ABANDONED          9
-#define STAT_INPROGRESS         10
 
 #define FREC_NOREBIND           1
 #define FREC_CHECKING_DISABLED  2
@@ -727,6 +726,7 @@ struct frec {
   struct blockdata *stash; /* Saved reply, whilst we validate */
   size_t stash_len;
   struct frec *dependent; /* Query awaiting internally-generated DNSKEY or DS query */
+  struct frec *next_dependent; /* list of above. */
   struct frec *blocking_query; /* Query which is blocking us. */
 #endif
   struct frec *next;