Include redisSock's persistent_id in persistent connection pool persistent_id string

[thor-son]

When use dbNumber 0 and not use select command after redis connect, pconnect return already selected db redisConn.
So use persistent_id for identified redisConn. But Not work.
This issue was opened. #1920
And not match in README.md description.

phpredis/README.md

Line 291 in ff30534

$redis->pconnect('127.0.0.1', 6379, 2.5, 'x'); // x is sent as persistent_id and would be another connection than the three before.

All connection pool contained or not persistent_id return same persistent_id.
Of course it can be solved by using redis.pconnect.pool_pattern, Default option users will have a hard time understanding why an issue occurs.
This issue start at 5.0.0 version's commit. 8206b14