String change in unattended-upgrades

[Michael Vogt]

Hi,

in order to fix a bug (well, a corner case condition when dpkg got
interrupted because of e.g. power-failure ) in unattended-upgrades I
had to add a string to explain the user the situation. 

I'm sorry for the inconvenience this causes you. Please note that the
translation for this is not super-important as its a corner case and
most people who see it (those who explicitely ask for mail from cron
or unattended-upgrades themself) are probably more technical. Desktop
users should never see the message, it will just fix the problem in
the background.

Cheers,
 Michael