Auth changes (currentLogin)

Hi!

I deleted the currentLogin column in the auth storage. currentLogin is now
only used internally. Therefore lastLogin won't be modified anymore
($lastLogin = $currentLogin). lastLogin now always contains the timestamp of
the last login and updateUserData() now updates only the lastLogin column
with $this->currentLogin (IMO to update other columns than lastLogin you
should use the admin functions).
I had to change the common auth class. That's why I applied the changes to
all three auth containers. I tested the db container already, but I haven't
tested the MDB and XML container yet. It would be kind if someone of you
could check them.

While testing the recent LU changes (_GREAT_ BC breaks since 0.61!) I fixed
a bug with force login in LiveUser.php (see CVS log). Seems that we need
some more testing before having a beta release ;-)

Regards
Bjoern