* 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.

doc/dev-notes.txt

@@ -100,6 +100,8 @@
   alter table ViewJobs drop column mayFail;
   alter table ViewJobs add column autorelease integer not null default 0;
 
+  alter table Builds add column nixExprInput text;
+  alter table Builds add column nixExprPath text;
 
   
 * Job selection: