aufs based upgrade tests

[Vincenzo Ciancia]

When doing something like this one should be careful because here you 
have a copy of all files that are modified during the upgrade. 
Applications keeping these files open will write to the old copies, and 
applications which reopen the file after the upgrade will not see this 
data. This may be dangerous and lead to unexpected behaviour.

Apart from that, as I ranted in the past, let me say that this is a very 
important change and I am really happy that ubuntu developers are making 
it happen.

Vincenzo