bug #3830 Generate an APC prefix based on __FILE__ (trsteel88)

This PR was submitted for the 2.4 branch but it was merged into the 2.3 branch instead (closes #3830).

Discussion
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Generate an APC prefix based on __FILE__

Relates to https://github.com/symfony/symfony-standard/issues/654

Commits
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55a7676 Generate an APC prefix based on __FILE__

components/class_loader/cache_class_loader.rst

@@ -37,8 +37,8 @@ ApcClassLoader
     // instance of a class that implements a findFile() method, like the ClassLoader
     $loader = ...;
     
-    // my_prefix is the APC namespace prefix to use
-    $cachedLoader = new ApcClassLoader('my_prefix', $loader);
+    // sha1(__FILE__) generates an APC namespace prefix
+    $cachedLoader = new ApcClassLoader(sha1(__FILE__), $loader);
     
     // register the cached class loader
     $cachedLoader->register();
@@ -60,8 +60,8 @@ it is straightforward::
     // instance of a class that implements a findFile() method, like the ClassLoader
     $loader = ...;
     
-    // my_prefix is the XCache namespace
-    $cachedLoader = new XcacheClassLoader('my_prefix', $loader);
+    // sha1(__FILE__) generates an XCache namespace prefix
+    $cachedLoader = new XcacheClassLoader(sha1(__FILE__), $loader);
     
     // register the cached class loader
     $cachedLoader->register();