Bug in 2.3.0p1 when using UseLogin

[michael at moria.de]

> 2.5.1p1 has been released, also we need to know what platform your
> attempting to do this on.

I installed 2.5.1p1, but it does not fix the bug.  I use Linux, but the
problem is platform-independent, see session.c:1124, where it changes
to the users UID, which it doesn't do if UseLogin is in effect, because
login(1) does so.  Line 1332 protects running xauth(1) from running as
root, but that breaks X11 forwarding when using UseLogin.

Michael