Only email responsible authors when the build has changed

Dependencies

• [2] Z6JLDTRW Fix typos
• [3] N5AS7EKY Include who-broke-the-build information in notification emails
• [4] K3HODXGH Check all inputs for blame but only email selected inputs
• [*] 5EQYVRWE Add a plugin mechanism

Change contents

• replacement in src/lib/Hydra/Plugin/EmailNotification.pm at line 83
  [3.248]→[2.0:39](∅→∅)
  − if (scalar keys %{$authors} > 0) {
  [3.248]

  [3.286]
  + my $prevBuild = getPreviousBuild($build);

  + if (scalar keys %{$authors} > 0 &&

  + ((!defined $prevBuild) || ($build->buildstatus != $prevBuild->buildstatus))) {