Description:
------------
The default php include_path cannot be appended to by using ${include_path}

I have a machine which has no include_path set in php.ini, the system picks
up the default include_path path from the build-defs.h during the build.

gopalv@delta:~$ /opt/php53/bin/php -v
PHP 5.3.4-dev (cli) (built: Oct 12 2010 18:47:42) 
Copyright (c) 1997-2010 The PHP Group
Zend Engine v2.3.0, Copyright (c) 1998-2010 Zend Technologies

gopalv@delta:~$ /opt/php53/bin/php -i | grep include_path
include_path => .:/opt/php53//lib/php => .:/opt/php53//lib/php

gopalv@delta:~$ cat php-bug.ini 
include_path=${include_path}:/tmp


gopalv@delta:~$ /opt/php53/bin/php -c php-bug.ini -i | grep include_path
include_path => :/tmp => :/tmp


Test script:
---------------
gopalv@delta:~$ cat php-bug.ini 
include_path=${include_path}:/tmp
gopalv@delta:~$ /opt/php53/bin/php -c php-bug.ini -i | grep include_path
include_path => :/tmp => :/tmp


Expected result:
----------------
include_path => .:/opt/php53//lib/php:/tmp => .:/opt/php53//lib/php:/tmp


Actual result:
--------------
include_path => :/tmp => :/tmp