1.0.0-rc.4

Fourth release candidate for 1.0.0; the app version is 0.9.10. 1.0.0-rc.3 (0.9.9) was not
released: its fixes are in here.

Changed

• A full restore over SFTP reads the packs ahead on a connection of its own, 32 requests in
  flight, into temporary files in the restore folder. From a Hetzner Storage Box to a server in
  Canada (122 ms) packs now come in at about 14 MiB/s instead of 2.8. More connections can be set
  with restore_sftp_connections (README). A part that cannot be read this way is read as
  before. Restores from other locations work as before.
• App store description: the line about Ensembia.

Fixed

• After a full restore stopped halfway, running it again with --force was refused when the
  database was already restored: Nextcloud then first wants occ upgrade. The guide and the
  error message now say so.
• A full restore of a backup made before 1.0.0-rc.2 with --skip-missing-tables failed on
  PostgreSQL with "relation ... does not exist": the left-out tables were still looked up to set
  their ID counters. It now skips them. A new test restores a backup made by 1.0.0-rc.1 on
  PostgreSQL and MariaDB.
• The app store showed old screenshots: it keeps a copy per URL, and the URLs always pointed at
  main. They now point at the release's tag.