Fix related changes after rebase

Given a stack of two commits C->P (child depends on parent), if P is
rebased or updated C should still considered to be a related change,
even if C has not yet been rebased onto P' (new P).

This was broken because we did not include all permutations of P
into the seed queue.

Bug: issue 2073
Change-Id: Ife954810ece39f44630b8c17a4f1b70192bd1611

gerrit-server/src/main/java/com/google/gerrit/server/change/GetRelated.java

@@ -227,7 +227,7 @@ public class GetRelated implements RestReadView<RevisionResource> {
       if (cId.equals(p.getId().getParentKey())) {
         try {
           RevCommit c = rw.parseCommit(ObjectId.fromString(
-              rsrc.getPatchSet().getRevision().get()));
+              p.getRevision().get()));
           if (!c.has(seenCommit)) {
             c.add(seenCommit);
             q.add(c.name());