Merge branch 'ns/tmp-objdir'

New interface into the tmp-objdir API to help in-core use of the
quarantine feature.

* ns/tmp-objdir:
  tmp-objdir: disable ref updates when replacing the primary odb
  tmp-objdir: new API for creating temporary writable databases

refs.c

@@ -2145,7 +2145,7 @@ int ref_transaction_prepare(struct ref_transaction *transaction,
 		break;
 	}
 
-	if (getenv(GIT_QUARANTINE_ENVIRONMENT)) {
+	if (refs->repo->objects->odb->disable_ref_updates) {
 		strbuf_addstr(err,
 			      _("ref updates forbidden inside quarantine environment"));
 		return -1;