Bug#457323: kdm: PreselectUser=None fails to inhibit reading a pre-existing user cache

[Justin Pryzby <jpryzby+d@quoininc.com>]

Package: kdm
Version: 4:3.5.8.dfsg.1-2
Severity: normal

After setting PreselectUser=None, a user was still preselected.  It
was necessary to [re]move /var/lib/kdm/kdmsts to avoid username
"preselection".

So it seems that PreselectUser=None fails to work as advertized:
	# "None" - do not preselect any user
However what it actually seems to do is: "avoid updating the
previous-username cache".

I think the effect of PreselectUser=None should be to avoid *reading*
the file.  Inhibiting its update is a possible 2ndary effect.