Since Exim version 4.90
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+GF/01 DEFER rather than ERROR on redis cluster MOVED response.
+ When redis_servers is set to a list of > 1 element, and the Redis servers
+ in that list are in cluster configuration, convert the REDIS_REPLY_ERROR
+ case of MOVED into a DEFER case instead, thus moving the query onto the
+ next server in the list. For a cluster of N elements, all N servers must
+ be defined in redis_servers.
+
JH/01 Replace the store_release() internal interface with store_newblock(),
which internalises the check required to safely use the old one, plus
the allocate and data copy operations duplicated in both (!) of the