Description:
------------
Started seeing more frequent Apache crashes after upgrade to PHP 7.0 for one of our applications which makes heavy use of apc cache. After investigation, found a reproduction script to trigger segmentation fault eventually.

Late apcu code inspection revealed that code doesn't check for memory allocation failures on many places. Typical case for example: string duplication fails in apcu_store(), code then inserts zval with NULL value into cache, then apcu_fetch() crashes when dereferencing the value.

I hope I've covered all necessary places in the patch, but surely would suggest close review. So far only the case triggered by the below test is really tested.

Test script:
---------------
<?php

/*
Might need tweaking to trigger the memory allocation failure

ini settings:
memory_limit = 4512M
apcu shared memory size default - 128M
*/

$f = str_repeat('c', 800 * 1024 * 1024 );

apcu_store('aaa', $f, 5);

$s = apcu_fetch('aaa');

echo ($s == $f) ? "same" : "different";


Expected result:
----------------
script running to completion, returning "same" if no memory problem, "different" if memory allocation failure in apc_fetch()

Actual result:
--------------
Segmentation fault: 11