relative include from symbolic linked file

[lumberjakel]

Description:
------------
On my development server I have a directory:
/var/

http://www/app

containing the file:
menu.inc
dbsettings.inc
and the symbolic links
db_mysql.inc -> /var/export/db_mysql.inc
subdir -> /var/export/subdir

In the directory /var/export:
db_mysql.inc
In the directory /var/export/subdir:
include.inc

The file db_mysql.inc has the following line:
require_once("dbsettings.inc");
The file include.inc has the following line:
require_once("../menu.inc");

What happens is that the include_path is ".", so the file ../menu.inc
cannot be found by include.inc

I tried to set the include_path to /var/

http://www/app.

This worked for the
file db_mysql.inc, but it didn't work for menu.inc. I tried to set the
include path to ".:/var/

http://www/app",

but then the file dbsettings.inc
couldn't be found.
I also tried "/var/

http://www/app:/var/www/app/subdir"

and lots of other
combinations.

On a release server the two directories are merged so there will be no
symlinks. (The problem I have does not occur on this server)

I googled lots of hours, but didn't find any thing useful.
I expected PHP to open the symlinked files as if they were actually
there.
Can I configure PHP to do so?

Reproduce code:
---------------
/var/export/db_mysql.inc:
require_once('dbsettings.inc');

/var/export/subdir/include.inc:
require_once('../menu.inc');

/var/

http://www/app/menu.inc:

$menu = array( ... );

/var/

http://www/app/dbsettings.inc:

$host = 'localhost';
$user = '...';
...

symlinks:
/var/

http://www/app/db_mysql.inc

-> /var/export/db_mysql.inc
/var/

http://www/app/subdir

-> /var/export/subdir

Expected result:
----------------
I expected PHP to open the symlinked files as if they were actually
there.

Actual result:
--------------
Warning: main(../menu.inc): failed to open stream: No such file or
directory in /var/export/subdir/include.inc on line 4

Fatal error: main(): Failed opening required '../menu.inc'
(include_path='/var/

http://www/app')

in /var/export/subdir/include.inc on line
4