Use pixz instead of bzip2 for compressing nars

Dependencies

• [2] GX2GISE2 Revert "Don't compress already-compressed files."
• [3] PMDWFZHW hydra-module.nix: Fix setting the logo
• [4] M4JUF5V6 Drop obsolete graphviz dependency
• [5] K4DKM74W release.nix use makeBinPath to construct PATH
• [6] ALIOF64I * Use IO::Handles instead of old school filehandles. This ensures
• [7] LOHWNXEJ Cleanup
• [8] 3PNG7NIB Remove trailing whitespace
• [9] L7RW467Z Add a test for darcs inputs.
• [10] T4LLYESZ * Nix expression for building Hydra.
• [11] AFNDUSGD Set Expires headers for Hydra's binary cache
• [12] 57Y7RG2A Update queryPathInfo calls
• [13] NYC3LZKH * Generate NAR archives on the fly. Necessary for producing channels
• [14] IDT3SO3P Generate *.narinfo files on the fly to support the binary cache substituter
• [15] UCJEI7YZ Don't compress already-compressed files.
• [*] D3MDJONY
• [*] 4J33F22T hydra-module.nix: Make it possible to add extra config lines

Change contents

• edit in hydra-module.nix at line 228
  [18.373]

  [3.81]
  + compress_num_threads 0
• replacement in release.nix at line 137
  [5.36]→[6.348:416](∅→∅),[6.348]→[6.348:416](∅→∅)
  − [ libxslt sqlite subversion openssh nix coreutils findutils
  [5.36]

  [4.0]
  + [ libxslt sqlite subversion openssh nix coreutils findutils pixz
• replacement in src/lib/Hydra/View/NARInfo.pm at line 24
  [6.1135]→[2.0:37](∅→∅)
  − $info .= "Compression: bzip2\n";
  [6.1135]

  [6.1269]
  + $info .= "Compression: xz\n";
• replacement in src/lib/Hydra/View/NixNAR.pm at line 10
  [6.597]→[6.597:641](∅→∅)
  − my $storePath = $c->stash->{storePath};
  [6.597]

  [6.3112]
  + my $storePath = $c->stash->{storePath};

  + my $numThreads = $c->config->{'compress_num_threads'};

  + my $pParam = ($numThreads > 0) ? "-p$numThreads" : "";
• replacement in src/lib/Hydra/View/NixNAR.pm at line 18
  [6.3115]→[2.38:95](∅→∅)
  − open $fh, "nix-store --dump '$storePath' | bzip2 |";
  [6.3115]

  [6.866]
  + open $fh, "nix-store --dump '$storePath' | pixz -0 $pParam |";