Disable database COMMENT field by default in all other DB Forge drivers

Signed-off-by: Zachary Flower <zach@ninjaninja.net>
diff --git a/system/database/drivers/sqlite3/sqlite3_forge.php b/system/database/drivers/sqlite3/sqlite3_forge.php
index a527e51..df05548 100644
--- a/system/database/drivers/sqlite3/sqlite3_forge.php
+++ b/system/database/drivers/sqlite3/sqlite3_forge.php
@@ -60,6 +60,13 @@
 	 */
 	protected $_null		= 'NULL';
 
+	/**
+	 * COMMENT value representation in CREATE/ALTER TABLE statements
+	 *
+	 * @var	string
+	 */
+	protected $_comment			= FALSE;
+
 	// --------------------------------------------------------------------
 
 	/**