Description:
------------
When open_basedir is set in php.ini, file_exists() will never return if called with an argument containing a ":/" or ":\\" without a corresponding drive letter.

Example:

file_exists("C:/foo.txt") => works
file_exists("C:\\foo.txt") => works

file_exists(":/foo.txt") never returns.
file_exists(":\\foo.txt") never returns.

Tested under Windows 2003 Server with SP2 and Windows XP Pro, both using Apache 2.2.6/mod_php. 

Reproduce code:
---------------
copy php.ini-dist to php.ini
set open_basedir = C:/

<?php
//Should print "no"
print file_exists("C:/foo.txt")?"yes\n":"no\n";

//Should also print "no" but never returns,
//causing high CPU, if open_basedir is set
print file_exists(":/foo.txt")?"yes\n":"no\n";
exit;
?>

Expected result:
----------------
no
no

Actual result:
--------------
no
file_exists() call never returns