Description:
------------
The behavior of rename() is inconsistent between Linux and Windows.

On Linux, the rename() function is atomic - you can rename() one file over an existing file, and the replacement is atomic.

On Windows, you cannot rename over an existing file.

Reproduce code:
---------------
<?php

file_put_contents("file1.txt", "this is file 1");
file_put_contents("file2.txt", "this is file 2");

rename("file1.txt", "file2.txt");

echo "reading file 2: ";
readfile("file2.txt");

?>

Expected result:
----------------
reading file 2: this is file 1


Actual result:
--------------
On Linux: (CORRECT)

reading file 2: this is file 1

On Windows: (INCORRECT)

Warning: rename(file1.txt,file2.txt) [function.rename]: File exists in C:\Web3\test\rename\test.php on line 6
reading file 2: this is file 2