Merge branch 'maint-1.5.5' into maint-1.5.6

* maint-1.5.5:
  revision traversal and pack: notice and die on missing commit

Conflicts:
	revision.c

diff --cc revision.c
index a68abec3f203d751db3eb4bce9c8e958abf3cc9e,07e5fcd86cfe6292bc21bbf0d6cc786e81ae02cc..3861470389cc8f154c071500a0f4cd169f0fc10d
--- 1/revision.c
--- 2/revision.c
+++ b/revision.c
@@@ -1598,8 -1560,9 +1598,9 @@@ static struct commit *get_revision_1(st
                        if (revs->max_age != -1 &&
                            (commit->date < revs->max_age))
                                continue;
 -                      if (add_parents_to_list(revs, commit, &revs->commits) < 0)
 +                      if (add_parents_to_list(revs, commit, &revs->commits, NULL) < 0)
-                               return NULL;
+                               die("Failed to traverse parents of commit %s",
+                                   sha1_to_hex(commit->object.sha1));
                }
  
                switch (simplify_commit(revs, commit)) {