DocBlocks for base DB classes

Partially fixes issue #1295.
diff --git a/system/database/DB_cache.php b/system/database/DB_cache.php
index 37d2dd0..b8f8995 100644
--- a/system/database/DB_cache.php
+++ b/system/database/DB_cache.php
@@ -35,8 +35,24 @@
  */
 class CI_DB_Cache {
 
+	/**
+	 * CI Singleton
+	 *
+	 * @var	object
+	 */
 	public $CI;
-	public $db;	// allows passing of db object so that multiple database connections and returned db objects can be supported
+
+	/**
+	 * Database object
+	 *
+	 * Allows passing of DB object so that multiple database connections
+	 * and returned DB objects can be supported.
+	 *
+	 * @var	object
+	 */
+	public $db;
+
+	// --------------------------------------------------------------------
 
 	/**
 	 * Constructor
@@ -59,7 +75,7 @@
 	/**
 	 * Set Cache Directory Path
 	 *
-	 * @param	string	the path to the cache directory
+	 * @param	string	$path	Path to the cache directory
 	 * @return	bool
 	 */
 	public function check_path($path = '')
@@ -95,7 +111,7 @@
 	 * Retrieve a cached query
 	 *
 	 * The URI being requested will become the name of the cache sub-folder.
-	 * An MD5 hash of the SQL statement will become the cache file name
+	 * An MD5 hash of the SQL statement will become the cache file name.
 	 *
 	 * @param	string	$sql
 	 * @return	string
@@ -154,8 +170,8 @@
 	/**
 	 * Delete cache files within a particular directory
 	 *
-	 * @param	string	$segment_one = ''
-	 * @param	string	$segment_two = ''
+	 * @param	string	$segment_one
+	 * @param	string	$segment_two
 	 * @return	void
 	 */
 	public function delete($segment_one = '', $segment_two = '')