New retry_reads_on_master option, when a read to the slave-redis instance fails (ie due to the redis instance still loading data), reads will fail-back to the master instance.
Confirm php 7.3 compatibility for pure-php redis connector
Compat bugfix for phpredis-v3 for exists() function. phpredis-v3 returns a bool, credis/phpredis-v4 return an int, this ensures all backend redis connectors return the same type for the exists function.
