Merge branch 'ab/struct-init'

Code cleanup around struct_type_init() functions.

* ab/struct-init:
  string-list.h users: change to use *_{nodup,dup}()
  string-list.[ch]: add a string_list_init_{nodup,dup}()
  dir.[ch]: replace dir_init() with DIR_INIT
  *.c *_init(): define in terms of corresponding *_INIT macro
  *.h: move some *_INIT to designated initializers

refs/packed-backend.c

@@ -1425,7 +1425,7 @@ static int packed_transaction_prepare(struct ref_store *ref_store,
 	 */
 
 	CALLOC_ARRAY(data, 1);
-	string_list_init(&data->updates, 0);
+	string_list_init_nodup(&data->updates);
 
 	transaction->backend_data = data;