hydra-build: Don't send a giant query to the database

Dependencies

• [2] MNZ67UXO If a build step fail, immediately fail all queued builds that depend on it
• [3] 6K5PBUUN Use buildEnv to combine Hydra's Perl dependencies
• [4] OG7BEM57
• [5] 4SJPAAJX Pass failing dependent builds to buildFinished
• [6] JGLE5BRN Add separate build step status codes for cached failures and timeouts
• [7] PMNWRTGJ Add multiple output support
• [*] T4LLYESZ * Nix expression for building Hydra.
• [*] 7YBYT2LQ
• [*] IW2LHCLL fixed email bug

Change contents

• edit in release.nix at line 95
  [3.910]

  [3.910]
  + SetScalar
• edit in src/script/hydra-build at line 14
  [11.30]

  [10.2987]
  + use Set::Scalar;
• replacement in src/script/hydra-build at line 45
  [2.346]→[2.346:404](∅→∅)
  − my @dependentDrvs = computeFSClosure(1, 0, $drvPath);
  [2.346]

  [2.404]
  + my $dependentDrvs = Set::Scalar->new(computeFSClosure(1, 0, $drvPath));
• replacement in src/script/hydra-build at line 52
  [2.516]→[2.516:590](∅→∅)
  − { drvpath => [ @dependentDrvs ], finished => 0, busy => 0 });
  [2.516]

  [4.15982]
  + { finished => 0, busy => 0 },

  + { columns => ["id", "project", "jobset", "job", "drvpath"] });
• edit in src/script/hydra-build at line 56
  [2.630]

  [2.630]
  + next unless $dependentDrvs->has($d->drvpath);