Merge branch 'ps/ref-backend-migration-optim'

The migration procedure between two ref backends has been optimized.

* ps/ref-backend-migration-optim:
  reftable: rename scratch buffer
  refs: adapt `initial_transaction` flag to be unsigned
  reftable/block: optimize allocations by using scratch buffer
  reftable/block: rename `block_writer::buf` variable
  reftable/writer: optimize allocations by using a scratch buffer
  refs: don't normalize log messages with `REF_SKIP_CREATE_REFLOG`
  refs: skip collision checks in initial transactions
  refs: use "initial" transaction semantics to migrate refs
  refs/files: support symbolic and root refs in initial transaction
  refs: introduce "initial" transaction flag
  refs/files: move logic to commit initial transaction
  refs: allow passing flags when setting up a transaction

builtin/tag.c

@@ -681,7 +681,7 @@ int cmd_tag(int argc,
 	}
 
 	transaction = ref_store_transaction_begin(get_main_ref_store(the_repository),
-						  &err);
+						  0, &err);
 	if (!transaction ||
 	    ref_transaction_update(transaction, ref.buf, &object, &prev,
 				   NULL, NULL,