The "old" FTP code made sure to just use 1 session, even when descending
into dependencies... I guess this feature is gone?
The problem with using only one session is that you either need to
extract packages to a temporary location first (what the old code did)
or reopen the package when the dependencies have been processed.
The former has a different can of worms as it can require quite a lot of
temporary space (certain cases for Qt4 etc needed over 500MB).
The latter adds a number of complications that aren't nice either.
Where this comes from is the per-IP limit on FTP sessions which is a bit
too low for the really big meta packages.