Add support for the COMMENT field in DBForge and MySQL Forge classes (pdo, mysql, and mysqli)

Signed-off-by: Zachary Flower <zach@ninjaninja.net>
diff --git a/system/database/drivers/mysql/mysql_forge.php b/system/database/drivers/mysql/mysql_forge.php
index 6f0d6c5..7053fa1 100644
--- a/system/database/drivers/mysql/mysql_forge.php
+++ b/system/database/drivers/mysql/mysql_forge.php
@@ -192,6 +192,7 @@
 			.$field['null']
 			.$field['default']
 			.$field['auto_increment']
+			.$field['comment']
 			.$field['unique']
 			.$extra_clause;
 	}