Adding fix for Cache causing App to do an directory scan when importi…

…ng a core cache engine. Since these operations occurred before the core configurations had be set, a directory scan was done on every request. This change also makes in not possible to override the core cache engines with app versions.

cake/libs/cache.php

@@ -196,11 +196,13 @@ function __loadEngine($name, $plugin = null) {
 		if ($plugin) {
 			return App::import('Lib', $plugin . '.cache' . DS . $name, false);
 		} else {
-			$app = App::import('Lib', 'cache' . DS . $name, false);
-			if (!$app) {
-				require LIBS . 'cache' . DS . strtolower($name) . '.php';
+			$core = App::core();
+			$path = $core['libs'][0] . 'cache' . DS . strtolower($name) . '.php';
+			if (file_exists($path)) {
+				require $path;
+				return true;
 			}
-			return true;
+			return App::import('Lib', 'cache' . DS . $name, false);
 		}
 	}