Input class improvements

- Disable register_globals replication on PHP 5.4+ (no longer exists).
- DocBlock improvements.
- Add missing changelog entry.
- Change user_agent() to return NULL when no value is found (for consistency with other fetcher methods).
diff --git a/system/core/Config.php b/system/core/Config.php
index 152e9af..642cee7 100644
--- a/system/core/Config.php
+++ b/system/core/Config.php
@@ -55,7 +55,7 @@
 	/**
 	 * List of paths to search when trying to load a config file.
 	 *
-	 * @used-by	CI_Loader	Must be public
+	 * @used-by	CI_Loader
 	 * @var		array
 	 */
 	public $_config_paths =	array(APPPATH);