disabling log_rotation_age feature.

Hi,

I'm reading about log_rotation_age.
And I noticed that the setting for disabling the feature is not clear.

The document tells us to set it to ZERO if we want to disable the feature.
However, the feature would be disabled if we set it less than one minute.

[Example]
*******************************************
$ grep log_rotation_age ${PGDATA}/postgresql.conf
#log_rotation_age = 1d # Automatic rotation of logfiles will
log_rotation_age = 10s # Automatic rotation of logfiles will

$ psql postgres
psql (9.5devel)
Type "help" for help.

postgres=# show log_rotation_age ;
log_rotation_age
------------------
0
(1 row)
*******************************************

I think this fact should be written on document for users.

[Fix Example]
*********
After this many minutes have elapsed, a new log file will
- be created. Set to zero to disable time-based creation of
+ be created. Set to zero or less than one minute to disable time-based
new log files.
*********

regards,
-----------------
Tomonari Katsumata