BUG #13879: include_dir directive not working

The following bug has been logged on the website:

Bug reference:      13879
Logged by:          Andreas Dewes
Email address:      andreas.dewes@7scientists.com
PostgreSQL version: 9.3.10
Operating system:   Ubuntu 14.04 LTS
Description:

It seems that the `include_dir` directive does not work at all in this
Postgres version. I tested this with a `postgresql.conf` file that looks
like this:

include_dir 'conf.d'

The subdirectory `conf.d` (which sits in the same directory as the
`postgresql.conf` file) contains the files `001_base.conf`,
`002_performance.conf`, `003_replication.conf`.

When I run `pg_lsclusters` (or any other Postgres command), I get `invalid
data directory error`. It therefore seems that the configuration files in
the `conf.d` directory do not get included at all.

If I replace the `include_dir` directive with three explicit `include
'conf.d/001_base.conf'`, ... directives everything works as expected. I also
checked the configuration files for errors to exclude that the loading fails
for that reason, they seem to be fine though (I also removed the 002_ and
003_ files for testing). The log file doesn't reveal any useful information
either. Using the absolute path name of the `conf.d` directory in the
include_dir statement does not help either. Directory and file permissions
are correctly set and the names of the configuration files all end with
`.conf`.

Any ideas?