[Hackday] [2.7] Add a deprecation note about Validator's ApcCache

[javiereguiluz]

NOTE: This issue is part of the "SymfonyCon 2014 Madrid Hackday" effort to add logs for every 2.7 deprecated feature. This is needed before removing those features in 3.0 version. Please, add you name in a comment of this issue if you are going to work on this.

If you need it, this Gist explains how to generate the deprecation note:

https://gist.github.com/javiereguiluz/a5514ec6cde2a63be441

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The class Symfony\Component\Validator\Mapping\Cache\ApcCache has been removed in favor of Symfony\Component\Validator\Mapping\Cache\DoctrineCache.

Before:

use Symfony\Component\Validator\Mapping\Cache\ApcCache;

$cache = new ApcCache('symfony.validator');

After:

use Symfony\Component\Validator\Mapping\Cache\DoctrineCache;
use Doctrine\Common\Cache\ApcCache;

$apcCache = new ApcCache();
$apcCache->setNamespace('symfony.validator');

$cache = new DoctrineCache($apcCache);

[kbsali]

i'll take that one.