[ci skip] DocBlocks for DB drivers' utility classes

Partially fixes issue #1295.
diff --git a/system/database/drivers/postgre/postgre_forge.php b/system/database/drivers/postgre/postgre_forge.php
index aac82c1..b08fa51 100644
--- a/system/database/drivers/postgre/postgre_forge.php
+++ b/system/database/drivers/postgre/postgre_forge.php
@@ -35,13 +35,20 @@
  */
 class CI_DB_postgre_forge extends CI_DB_forge {
 
+	/**
+	 * DROP TABLE statement
+	 *
+	 * @var	string
+	 */
 	protected $_drop_table	= 'DROP TABLE IF EXISTS %s CASCADE';
 
+	// --------------------------------------------------------------------
+
 	/**
 	 * Process Fields
 	 *
 	 * @param	mixed	$fields
-	 * @param	array	$primary_keys = array()
+	 * @param	array	$primary_keys
 	 * @return	string
 	 */
 	protected function _process_fields($fields, $primary_keys = array())
@@ -195,7 +202,7 @@
 	 * @param	string	$alter_type	the ALTER type (ADD, DROP, CHANGE)
 	 * @param	string	$table		the table name
 	 * @param	string	$fields		the column definition
-	 * @param	string	$after_field = ''
+	 * @param	string	$after_field
 	 * @return	string
 	 */
 	protected function _alter_table($alter_type, $table, $fields, $after_field = '')
diff --git a/system/database/drivers/postgre/postgre_utility.php b/system/database/drivers/postgre/postgre_utility.php
index 96cd90e..bae1c67 100644
--- a/system/database/drivers/postgre/postgre_utility.php
+++ b/system/database/drivers/postgre/postgre_utility.php
@@ -35,13 +35,26 @@
  */
 class CI_DB_postgre_utility extends CI_DB_utility {
 
+	/**
+	 * List databases statement
+	 *
+	 * @var	string
+	 */
 	protected $_list_databases	= 'SELECT datname FROM pg_database';
-	protected $_optimize_table	= 'REINDEX TABLE %s';
 
 	/**
-	 * Postgre Export
+	 * OPTIMIZE TABLE statement
 	 *
-	 * @param	array	Preferences
+	 * @var	string
+	 */
+	protected $_optimize_table	= 'REINDEX TABLE %s';
+
+	// --------------------------------------------------------------------
+
+	/**
+	 * Export
+	 *
+	 * @param	array	$params	Preferences
 	 * @return	mixed
 	 */
 	protected function _backup($params = array())