[MERGE] Fix bug causing file deltas to be added to wrong versionedfile

[Aaron Bentley]

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John Arbash Meinel wrote:
> John Arbash Meinel has voted approve.
> Status is now: Approved
> Comment:
> This seems pretty serious. Are you sure it isn't something we need to
> merge back into 0.90?

It's worth considering.  It can insert unreferenced data into knits,
which is gross but not dangerous.  For it to insert referenced data:

1. the parent of the data would have to be referenced
2. applying the mpdiff to the parent would have to produce the correct SHA1.

The only cases I can think of where that would happen would be if the
revision being introduced had no parents.

So it's really a question of: where do we want to be conservative?  Less
code change, or less reliance on my analysis that it's not dangerous?

On balance, I'd like to see it in 0.90.

> I can see your logic here, and it seems fine (it was just that you
> weren't clearing out the 'last file' information, right?)

Yes.  I was opening the knit early so that I could discard unneeded
records, but in this case I was forgetting to switch to the next knit.

Aaron
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