xopen() wants 2 arguments unless you're creating a file, in which case you

xopen() wants 2 arguments unless you're creating a file, in which case you
need 3.  Doing varargs for this doesn't really appeal to me (bugs in waiting)
so I made an xcreate() that takes 3 args, and had xopen() call it with 0 for
the third argument.  That way, if we feed O_CREAT to xopen() the permission
000 result should be easy to spot.