Description:
------------
When compiling cached opcode, APC does not check if functions 
are already declared.

This seems to be happening because the return value of 
install_function() in cached_compile() is not checked.

If you need more testing or patches, please let me know. I'd 
be glad to help.

Reproduce code:
---------------
Step one:

~# cat index.php

<?php
require('file2.php');
test();

~# cat file2.php

<?php 
function test() { echo 'test() called from file2.php'; }

Load index.php in a browser.

Step two:

~# cat index.php

<?php
require('file1.php');
require('file2.php');
test();

~# cat file1.php

<?php 
function test() { echo 'test() called from file1.php'; }

~# cat file2.php

<?php 
function test() { echo 'test() called from file2.php'; }

Reload index.php in a browser.

Expected result:
----------------
Fatal error: Cannot redeclare test() (previously declared in 
~/file1.php:2) in ~/file2.php on line 2

Actual result:
--------------
test() called from file1.php