Encapsulate require_once to avoid name space bleedind

The script required by require_once might use variable names like $app
which will conflict with the code that follows.

This fix encapsulates require_once into its own function to avoid such
issues.

lib/private/app.php

@@ -92,7 +92,7 @@ public static function loadApp($app, $checkUpgrade = true) {
 			if ($checkUpgrade and self::shouldUpgrade($app)) {
 				throw new \OC\NeedsUpdateException();
 			}
-			require_once $app . '/appinfo/app.php';
+			self::requireAppFile($app);
 			if (self::isType($app, array('authentication'))) {
 				// since authentication apps affect the "is app enabled for group" check,
 				// the enabled apps cache needs to be cleared to make sure that the
@@ -103,6 +103,16 @@ public static function loadApp($app, $checkUpgrade = true) {
 		}
 	}
 
+	/**
+	 * Load app.php from the given app
+	 *
+	 * @param string $app app name
+	 */
+	private static function requireAppFile($app) {
+		// encapsulated here to avoid variable scope conflicts
+		require_once $app . '/appinfo/app.php';
+	}
+
 	/**
 	 * check if an app is of a specific type
 	 *