BUG #11595: PostgreSQL applies intermediate configuration files

The following bug has been logged on the website:

Bug reference: 11595
Logged by: Anh Huynh
Email address: kyanh(at)theslinux(dot)org
PostgreSQL version: 9.3.5
Operating system: Ubuntu 14.04 LTS
Description:

Problem
=======

When a configuration directive is declared multiple times, PostgreSQL will
apply the intermediate configuration and generate useless error message.

Expected behavior
=================

PostgresSQL uses the last declaration of a setting in its configuration.

Proof of the problem
====================

[code]
$ sudo cat /etc/postgresql/9.3/main/conf.d.no-puppet/log.conf

log_line_prefix = '1 [%t] '
log_line_prefix = '2 [%t] '
log_line_prefix = '3 [%t] '

$ sudo /etc/init.d/postgresql reload
* Reloading PostgreSQL 9.3 database server
...done.

$ grep log_line_prefix /var/log/postgresql/postgresql-9.3-main.log

1 [2014-10-06 03:39:53 UTC] LOG: parameter "log_line_prefix" changed to "1
[%t] "
2 [2014-10-06 03:39:53 UTC] LOG: parameter "log_line_prefix" changed to "2
[%t] "
3 [2014-10-06 03:39:53 UTC] LOG: parameter "log_line_prefix" changed to "3
[%t] "

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