Bug#622701: Message is due to changelog not always making it into the pool

[Dominique Brazziel]

	I turned on update-manager debug logging and saw 
the HTTP 404 error for every changelog that failed to download
so the cause is, indeed, because the changelogs are not
yet in the respective pool subdirectories (main, contrib
or non-free).  I am running mixed testing/unstable so
this makes sense (I guess).  It just seems as if the
failure instances are occurring more and more, I barely
get one out of fifteen any more.

	OK to close.