Spelling fixes - `wether` to `whether`

Interestingly `wether` means a castrated ram in old English
diff --git a/system/database/DB_query_builder.php b/system/database/DB_query_builder.php
index 1ac9af9..531ca9e 100644
--- a/system/database/DB_query_builder.php
+++ b/system/database/DB_query_builder.php
@@ -324,7 +324,7 @@
 	 * @param	string
 	 * @param	string	the join condition
 	 * @param	string	the type of join
-	 * @param	string	wether not to try to escape identifiers
+	 * @param	string	whether not to try to escape identifiers
 	 * @return	object
 	 */
 	public function join($table, $cond, $type = '', $escape = NULL)