[pgpool-hackers: 4041] Enable sr_check_period by default

[Tatsuo Ishii]

Currently the compile time default for sr_check_period is 0, which
means it is disabled by default. I propose to change it to be enabled
by the following reasons:

1) it's already enabled by default in pgpool.conf.sampe-stream.

2) Some features rely on sr_check: namely delay_threshold,
   prefer_lower_delay_standby, log_standby_delay and auto_failback.

3) sr_check_database and sr_check_password are mandatory even if
   sr_check_period is disabled.

I think sr_check_period is basically useful for all streaming
replication users. The only exception is AWS Aurora users because
sr_check does not work on Aurora.

So I would like to propose to change the compile time default for
sr_check_period from 0 to 10 (the value is used in
pgpool.conf.sample-stream) for upcoming Pgpool-II 4.3.

Barring no objection, I will make the change.
--
Tatsuo Ishii
SRA OSS, Inc. Japan
English: http://www.sraoss.co.jp/index_en.php
Japanese:http://www.sraoss.co.jp