Create failed build steps for cached failures

Dependencies

• [2] OCZ4LSGG Automatically retry aborted builds
• [3] RYTQLATY Keep track of failed paths in the Hydra database
• [4] MSIHMO45 Tweak build steps
• [*] 24BMQDZA Start of single-process hydra-queue-runner

Change contents

• replacement in src/hydra-queue-runner/hydra-queue-runner.cc at line 1162
  [3.1743]→[2.4908:4952](∅→∅)
  − if (!cachedFailure && !retry) {
  [3.1743]

  [3.1777]
  + if (!retry) {
• replacement in src/hydra-queue-runner/hydra-queue-runner.cc at line 1164
  [3.1778]→[3.1778:1883](∅→∅)
  − /* Create failed build steps for every build that depends

  − on this. */
  [3.1778]

  [3.1883]
  + /* Create failed build steps for every build that

  + depends on this. For cached failures, only create a

  + step for builds that don't have this step as

  + top-level (otherwise the user won't be able to see

  + what caused the build to fail). */
• edit in src/hydra-queue-runner/hydra-queue-runner.cc at line 1171
  [3.1983]

  [2.4953]
  + if (cachedFailure && build2->drvPath == step->drvPath) continue;