[ci skip] DocBlocks for DB drivers' driver classes

Partially fixes issue #1295.
diff --git a/system/database/drivers/mysqli/mysqli_driver.php b/system/database/drivers/mysqli/mysqli_driver.php
index 2e61a23..7d2507b 100644
--- a/system/database/drivers/mysqli/mysqli_driver.php
+++ b/system/database/drivers/mysqli/mysqli_driver.php
@@ -41,25 +41,46 @@
  */
 class CI_DB_mysqli_driver extends CI_DB {
 
+	/**
+	 * Database driver
+	 *
+	 * @var	string
+	 */
 	public $dbdriver = 'mysqli';
-	public $compress = FALSE;
-
-	// The character used for escaping
-	protected $_escape_char = '`';
-
-	protected $_random_keyword = ' RAND()'; // database specific random keyword
 
 	/**
+	 * Compression flag
+	 *
+	 * @var	bool
+	 */
+	public $compress = FALSE;
+
+	/**
+	 * DELETE hack flag
+	 *
 	 * Whether to use the MySQL "delete hack" which allows the number
 	 * of affected rows to be shown. Uses a preg_replace when enabled,
 	 * adding a bit more processing to all queries.
+	 *
+	 * @var	bool
 	 */
 	public $delete_hack = TRUE;
 
+	// --------------------------------------------------------------------
+
 	/**
-	 * Non-persistent database connection
+	 * Identifier escape character
 	 *
-	 * @param	bool
+	 * @var	string
+	 */
+	protected $_escape_char = '`';
+
+	// --------------------------------------------------------------------
+
+	/**
+	 * Database connection
+	 *
+	 * @param	bool	$persistent
 	 * @return	object
 	 * @todo	SSL support
 	 */
@@ -111,7 +132,7 @@
 	/**
 	 * Select the database
 	 *
-	 * @param	string	database name
+	 * @param	string	$database
 	 * @return	bool
 	 */
 	public function db_select($database = '')
@@ -135,7 +156,7 @@
 	/**
 	 * Set client character set
 	 *
-	 * @param	string
+	 * @param	string	$charset
 	 * @return	bool
 	 */
 	protected function _db_set_charset($charset)
@@ -162,7 +183,7 @@
 	/**
 	 * Execute the query
 	 *
-	 * @param	string	an SQL query
+	 * @param	string	$sql	an SQL query
 	 * @return	mixed
 	 */
 	protected function _execute($sql)
@@ -177,7 +198,7 @@
 	 *
 	 * If needed, each database adapter can prep the query string
 	 *
-	 * @param	string	an SQL query
+	 * @param	string	$sql	an SQL query
 	 * @return	string
 	 */
 	protected function _prep_query($sql)
@@ -197,7 +218,7 @@
 	/**
 	 * Begin Transaction
 	 *
-	 * @param	bool	$test_mode = FALSE
+	 * @param	bool	$test_mode
 	 * @return	bool
 	 */
 	public function trans_begin($test_mode = FALSE)
@@ -263,8 +284,8 @@
 	/**
 	 * Escape String
 	 *
-	 * @param	string
-	 * @param	bool	whether or not the string will be used in a LIKE condition
+	 * @param	string	$str
+	 * @param	bool	$like	Whether or not the string will be used in a LIKE condition
 	 * @return	string
 	 */
 	public function escape_str($str, $like = FALSE)
@@ -323,7 +344,7 @@
 	 *
 	 * Generates a platform-specific query string so that the table names can be fetched
 	 *
-	 * @param	bool
+	 * @param	bool	$prefix_limit
 	 * @return	string
 	 */
 	protected function _list_tables($prefix_limit = FALSE)
@@ -345,7 +366,7 @@
 	 *
 	 * Generates a platform-specific query string so that the column names can be fetched
 	 *
-	 * @param	string	the table name
+	 * @param	string	$table
 	 * @return	string
 	 */
 	protected function _list_columns($table = '')
@@ -358,7 +379,7 @@
 	/**
 	 * Returns an object with field data
 	 *
-	 * @param	string	the table name
+	 * @param	string	$table
 	 * @return	object
 	 */
 	public function field_data($table = '')
@@ -417,9 +438,9 @@
 	 *
 	 * Generates a platform-specific batch update string from the supplied data
 	 *
-	 * @param	string	the table name
-	 * @param	array	the update data
-	 * @param	string	the where key
+	 * @param	string	$table	Table name
+	 * @param	array	$values	Update data
+	 * @param	string	$index	WHERE key
 	 * @return	string
 	 */
 	protected function _update_batch($table, $values, $index)