• BuildSources= are now mounted when we install packages so local
  packages can be made available in the sandbox.
• Fixed check to see if we're running as root which makes sure we don't
  do shared mounts when running as root.
• The extension release file is now actually written when building
  system or configuration extensions.
• The nspawn settings are copied to the output directory again.
• Incremental caching is now skipped when Overlay= is enabled as this
  combination isn't supported.
• The SELinux relabel check is more granular and now checks for all
  required files instead of just whether there's a policy configured.
• qemu-system-xxx binaries are now preferred over the generic qemu
  and qemu-kvm binaries.
• Grub tools from the tools tree are now used to install grub instead of
  grub tools from the image itself. The grub tools were added to the
  default tools trees as well.
• The pacman keyring in tools trees is now only populated from the
  Arch Linux keyring (and not the Debian/Ubuntu ones anymore).
• gpg is allowed to access /run/pscsd/pscsd.comm on the host if it
  exists to allow interaction with smartcards.