Release 1.10.0

This is the first stable release after the 1.9.x unstable series.
The major new feature in this series compared to 1.8 is the support
for the new repo format which should make updates faster and download
less data.

This release also contains the security fixes from 1.8.5, so everyone
on the 1.9.x series should update immediately.

Other changes since 1.9.3:

• The systemd generator snippets now call flatpak --print-updated-env
  in place of a bunch of shell for better login performance.
• The .profile snippets now disable GVfs when calling flatpak to
  avoid spawning a gvfs daemon when logging in via ssh.
• Build fixes for GCC 11.
• Flatpak now finds the pulseaudio sockets better in uncommon
  configurations.
• Sandboxes with network access it now also has access to the
  systemd-resolved socket to do dns lookups.
• Flatpak supports unsetting env vars in the sandbox using --unset-env,
  and --env=FOO= now sets FOO to the empty string instead of
  unsetting it.
• Similarly the spawn portal has an option to unset an env var.
• The spawn portal now has an option to share the pid namespace
  with the sub-sandbox.

$ sha256sum flatpak-1.10.0.tar.xz 
c70215792b7cbece83c489dab86adc9bfaf9b140c506affe2a48c92afa3d69b7  flatpak-1.10.0.tar.xz