Merge branch 'kn/ref-transaction-symref'

Updates to symbolic refs can now be made as a part of ref
transaction.

* kn/ref-transaction-symref:
  refs: remove `create_symref` and associated dead code
  refs: rename `refs_create_symref()` to `refs_update_symref()`
  refs: use transaction in `refs_create_symref()`
  refs: add support for transactional symref updates
  refs: move `original_update_refname` to 'refs.c'
  refs: support symrefs in 'reference-transaction' hook
  files-backend: extract out `create_symref_lock()`
  refs: accept symref values in `ref_transaction_update()`

walker.c

@@ -326,7 +326,7 @@ int walker_fetch(struct walker *walker, int targets, char **target,
 		strbuf_reset(&refname);
 		strbuf_addf(&refname, "refs/%s", write_ref[i]);
 		if (ref_transaction_update(transaction, refname.buf,
-					   oids + i, NULL, 0,
+					   oids + i, NULL, NULL, NULL, 0,
 					   msg ? msg : "fetch (unknown)",
 					   &err)) {
 			error("%s", err.buf);