Use PostgreSQL 9.5

Dependencies

• [2] ICYJNJWH Revert "Move build logic for the core hydra package into its own default.nix."
• [3] UGA45FNC Add a plugin for backing up builds in s3
• [4] ZXVPPARR Cleanup
• [5] CLL3LBCD services.hydra -> services.hydra-dev
• [6] HPIJ35SG
• [7] WQ2VQ7H3 Use hydra-module.nix in the tests
• [8] GIBXI3X2 preHook -> shellHook
• [9] LOHWNXEJ Cleanup
• [*] T4LLYESZ * Nix expression for building Hydra.

Change contents

• replacement in release.nix at line 27
  [3.384]→[3.384:439](∅→∅)
  − services.postgresql.package = pkgs.postgresql92;
  [3.384]

  [3.0]
  + services.postgresql.package = pkgs.postgresql95;
• replacement in release.nix at line 134
  [2.2604]→[2.2604:2651](∅→∅)
  − postgresql92 # for running the tests
  [2.2604]

  [2.2651]
  + postgresql95 # for running the tests
• replacement in release.nix at line 246
  [3.341]→[3.341:400](∅→∅)
  − services.postgresql.package = pkgs.postgresql92;
  [3.341]

  [3.400]
  + services.postgresql.package = pkgs.postgresql95;