Now that we have xopen3(), it's just plain unclean to have xopen() with

Now that we have xopen3(), it's just plain unclean to have xopen() with
O_CREAT.  Two users are still doing it (and thus getting permissions 777),
I'm not sure what permissions they should be using but here they are
changed to xopen3().  This costs us a dozen or so bytes, but removing the
777 from xopen() should get some of that back.