Description:
------------
Using some custom include paths does probably not effect file_exists

Reproduce code:
---------------
<?php
// stripped down code of that what I'm using
// create a file: $rootPath/library/Berg/file.php you want to check

// this below is $rootPath/application/bootstrap.php
$rootPath = dirname(dirname(__FILE__)) . DIRECTORY_SEPARATOR;

set_include_path($rootPath . 'library' . PATH_SEPARATOR .
                 get_include_path());

var_dump(file_exists('Berg/file.php')) . '<br />';     // result false
var_dump(file_exists($rootPath . '/library/file.php')) // result true

require('Berg/file.php');                 // works
require($rootPath . '/library/file.php'); // works

?>

Expected result:
----------------
I expect both var_dumps to return true

Actual result:
--------------
The one using the include path (or actually does not) gives false instead of true.