Don't repeat links to build step logs

Dependencies

• [2] ZH6B56XR Try harder to find build logs
• [3] VG4QG336 Remove tablesorter
• [4] BIVZGPUT Optimise clickable rows
• [5] PMNWRTGJ Add multiple output support
• [6] 2GUAKGTB Fix indentation of build.tt
• [*] J5UVLXOK * Start of a basic Catalyst web interface.

Change contents

• replacement in src/root/build.tt at line 21
  [3.11774]→[3.11774:11819](∅→∅)
  − [% FOREACH step IN build.buildsteps %]
  [3.11774]

  [3.11819]
  + [% FOREACH step IN build.buildsteps.reverse %]
• replacement in src/root/build.tt at line 23
  [3.11941]→[2.2518:2567](∅→∅)
  − [% has_log = buildStepLogExists(step);
  [3.11941]

  [3.0]
  + [% has_log = seen.${step.drvpath} ? 0 : buildStepLogExists(step);

  + seen.${step.drvpath} = 1;