Add an inexpensive liveness check and make challenge/response optional

See phpredis#1742 and countless other persistent connection issues.

Author: michael-grunder

library.c

@@ -1810,6 +1810,8 @@ redis_sock_check_liveness(RedisSock *redis_sock)
     /* Check socket liveness using 0 second timeout */
     if (php_stream_set_option(redis_sock->stream, PHP_STREAM_OPTION_CHECK_LIVENESS, 0, NULL) != PHP_STREAM_OPTION_RETURN_OK) {
         return FAILURE;
+    } else if (!INI_INT("redis.pconnect.echo_check_liveness")) {
+        return SUCCESS;
     }
 
     if (redis_sock->auth) {

redis.c

@@ -90,6 +90,7 @@ PHP_INI_BEGIN()
     /* redis pconnect */
     PHP_INI_ENTRY("redis.pconnect.pooling_enabled", "1", PHP_INI_ALL, NULL)
     PHP_INI_ENTRY("redis.pconnect.connection_limit", "0", PHP_INI_ALL, NULL)
+    PHP_INI_ENTRY("redis.pconnect.echo_check_liveness", "1", PHP_INI_ALL, NULL)
 
     /* redis session */
     PHP_INI_ENTRY("redis.session.locking_enabled", "0", PHP_INI_ALL, NULL)