* apt-inst/contrib/extracttar.cc:

* apt-inst/contrib/extracttar.cc:
  - fix fd leak for zero size files (thanks to Bill Broadley for
    reporting this bug)
* apt-pkg/acquire-item.cc:
  - remove zero size files on I-M-S hit
* methods/https.cc:
  - only send LastModified if we actually have one
  - send range request with if-range
  - delete failed downloads
* apt-pkg/deb/dpkgpm.{cc,h}:
  - merged dpkg-log branch, this lets you specify a
    Dir::Log::Terminal file to log dpkg output to
    (ABI break)
* merged apt--sha256 branch to fully support the new
  sha256 checksums in the Packages and Release files
  (ABI break)
* Applied patch from Aurelien Jarno <aurel32@debian.org> to fix wrong
  directory downloading on non-linux architectures (closes: #435597)