* Store the jobset's nixExprPath and nixExprInput fields in a build to

allow it to be cloned (re-executed with modified inputs) later and
  to provide some traceability.

src/script/hydra_scheduler.pl

@@ -304,6 +304,8 @@ sub checkJob {
             , outpath => $outPath
             , system => $job->{system}
             , iscurrent => 1
+            , nixexprinput => $jobset->nixexprinput
+            , nixexprpath => $jobset->nixexprpath
             });
 
         print "added to queue as build ", $build->id, "\n";