Comment 10 for bug 368418

Summary of where we are:

 * the problem is that missing parent inventories aren't necessarily a problem, so the check introduced in r4307 is too strict. Ghosts cause missing parents, but can do so harmlessly. The actual problem the code wants to catch is when we have an inventory but not all the texts it introduces. i.e. for every text version in an inventory in a possibly stacked repo, we require that either a parent inventory also references that version (so we know the current inventory didn't introduce it) or that that text version is present in this repository.
 * I have a branch with a tentative fix. It certainly copes with the ghosts in bzr.dev, but obviously I want to make sure it's robust for all cases...