Comment 10 for bug 391411

Talking this over with Robert:

1 - Rather than copying all history when fetching, we could fetch the tip from a Repository configured with the fallback to a Repository with no fallbacks, asking for ghosts to be filled.

2 - We may need to specially check that fetching in this case brings across all the needed CHKMap inventory pages; that's probably not covered by my current test because the inventory is too small. (That could be split to a separate bug.)