[imp] access to IMP w/o a horde generated login screen

[Liam Hoekenga]

> > I've got hordeauth set to true, and I'm still getting presented w/ a
> > login screen.  Is this because the "auto" auth mechanism doesn't collect
> > a password, and IMP thinks it needs a password?
> 
> Correct. You should use the http authentication driver instead that should
> work out of the box for your case and sets a password credential.

Ok, I'm using a modified version of the http authentication driver replacing
$_SERVER['PHP_AUTH_USER'] with $_SERVER['REMOTE_USER'],  removing the check for
$_SERVER['PHP_AUTH_PW'] and making up a value for 'password' in the
Auth::setAuth statement (as we don't set either PHP_AUTH_USER or PHP_AUTH_PW,
and don't really need a password).

The initial launch of IMP is just fine.  It looks like the alternate_login
doesn't get invoked when you logout of IMP, and then hit the browser's back
button from whatever logout screen you're at (horde, or redirect_at_logout). 
It seems to me that if you define an alternate_login, it should get used
everytime a login occurs.

Liam