Description:
------------
PHP Version: 5.3.2-1ubuntu4.7

When using an include() statement within an if statement, PHP always fails with a seemingly blank input.

However, when used normally (obviously) it works fine, and when assigning the return value to a variable and then testing the value of the variable, include() works as intended.

Something that may or may not be a factor in this bug is that I have appended to the default include path; however, logically in all test cases (both in the actual project and the test script to create this bug report) this seems irrelevant to the bug.

Test script:
---------------
<?php
/*
	$v = include_once("blank.php");
	if(!$v)
		echo "FAILED";
	else
		echo "SUCCESS";
*/

if( include_once("blank.php") != true)
	echo "FAILED";
else
	echo "SUCCESS";

?>		

Expected result:
----------------
As is, the script should run just like a normal function; why it behaves in this matter only within in an if-then statement is the bug.

The script above -should- output FAILED if there is not a script entitled "blank.php", and SUCCESS if there is.

Actual result:
--------------
The script above, as-is, believes there is a blank string being inputted into the include() call, when in reality there is a perfectly valid filename. If you comment out the second half of the script and uncomment the first part, it works perfectly fine.

Error message:

Warning: include_once(/natoga/website/www/dev) [function.include-once]: failed to open stream: Not a directory in /natoga/website/www/dev/includeoncebug.php on line 10

Warning: include_once() [function.include]: Failed opening '' for inclusion (include_path='.:/usr/share/php:/usr/share/pear:/natoga/website/www/res') in /natoga/website/www/dev/includeoncebug.php on line 10