calculate hashes while downloading in https

calculate hashes while downloading in https

We do this in HTTP already to give the CPU some exercise while the disk
is heavily spinning (or flashing?) to store the data avoiding the need
to reread the entire file again later on to calculate the hashes – which
happens outside of the eyes of progress reporting, so you might ended up
with a bunch of https workers 'stuck' at 100% while they were busy
calculating hashes.

This is a bummer for everyone using apt as a connection speedtest as the
https method works slower now (not really, it just isn't reporting done
too early anymore).