Browsing Dutch translation

For most, don't do anything special.  Show generic 'unknown error'
message, but provide the exception text for better bug reports.
Plus, sometimes it may clue the user in to what's wrong.
But first, try to restart without a cache, since that seems to quite
frequently fix odd metadata errors with duplicity.  If we hit an error
a second time, we'll show the unknown error message.
Should emit some sort of error...