Note to self 2: Do as you preach. Test!

lib/base.php

@@ -570,7 +570,7 @@ class OC {
 			}
 			// NOTE: This will be replaced to use OCP
 			$userSession = \OC_User::getUserSession();
-			$userSession->listen('postLogin', array('OC\Cache\File', 'loginListener'));
+			$userSession->listen('postLogin', '\OC\Cache\File', 'loginListener');
 		}
 	}
 

lib/cache.php

@@ -6,7 +6,7 @@
  * See the COPYING-README file.
  */
 
-namespace OC\Cache;
+namespace OC;
 
 class Cache {
 	/**
@@ -24,7 +24,7 @@ class Cache {
 	 */
 	static public function getGlobalCache() {
 		if (!self::$global_cache) {
-			self::$global_cache = new FileGlobal();
+			self::$global_cache = new Cache\FileGlobal();
 		}
 		return self::$global_cache;
 	}
@@ -35,7 +35,7 @@ class Cache {
 	 */
 	static public function getUserCache() {
 		if (!self::$user_cache) {
-			self::$user_cache = new File();
+			self::$user_cache = new Cache\File();
 		}
 		return self::$user_cache;
 	}

lib/cache/fileglobal.php

@@ -10,7 +10,7 @@ namespace OC\Cache;
 
 class FileGlobal {
 	static protected function getCacheDir() {
-		$cache_dir = get_temp_dir().'/owncloud-'.OC_Util::getInstanceId().'/';
+		$cache_dir = get_temp_dir().'/owncloud-' . \OC_Util::getInstanceId().'/';
 		if (!is_dir($cache_dir)) {
 			mkdir($cache_dir);
 		}

lib/legacy/cache.php

@@ -6,5 +6,5 @@
  * See the COPYING-README file.
  */
 
-class Cache extends OC\Cache {
+class OC_Cache extends \OC\Cache {
 }