Use new 64bit vagrantbox.
Replaced default mirror inside Vagrant, now using http.debian.net.
Removed sources.list check (now it always exists in Vagrant).
Added patch for updating live-build binary_iso in build system.
Updated digabi-dev package: added patch for live-build.
Added prerm script.
Merge branch 'fix-lb-syslinux6'

* fix-lb-syslinux6:
  Added prerm script.
  Updated digabi-dev package: added patch for live-build.
  Added patch for updating live-build binary_iso in build system.