minor #8057 fix variable being overwritten (xabbuh)

This PR was merged into the 2.8 branch.

Discussion
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fix variable being overwritten

This fixes #7887.

Commits
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a08a8c4 fix variable being overwritten

Author: xabbuh

performance.rst

@@ -138,13 +138,15 @@ If you're using the Standard Distribution, make the following changes::
     
     use Symfony\Component\ClassLoader\ApcClassLoader;
 
-    $loader = require __DIR__.'/../app/autoload.php';
+    // do not use $loader as a variable name here as it would
+    // be overwritten when loading the bootstrap.php.cache file
+    $classLoader = require __DIR__.'/../app/autoload.php';
     include_once __DIR__.'/../app/bootstrap.php.cache';
 
     // Use APC for autoloading to improve performance
     // Change 'sf2' by the prefix you want in order
     // to prevent key conflict with another application
-    $loader = new ApcClassLoader('sf2', $loader);
+    $loader = new ApcClassLoader('sf2', $classLoader);
     $loader->register(true);
 
     // ...