Merge branch 'js/maint-fast-export-mark-error' into maint

"git fast-export" did not give a readable error message when the same
mark erroneously appeared twice in the --import-marks input.

builtin/fast-export.c

@@ -610,7 +610,7 @@ static void import_marks(char *input_file)
 			die ("Could not read blob %s", sha1_to_hex(sha1));
 
 		if (object->flags & SHOWN)
-			error("Object %s already has a mark", sha1);
+			error("Object %s already has a mark", sha1_to_hex(sha1));
 
 		mark_object(object, mark);
 		if (last_idnum < mark)