[PATCH] changelog: make sure datafile is 00changelog.d

[Jun Wu]

Excerpts from Gregory Szorc's message of 2017-05-17 20:09:53 -0700:
> Hmmm. I suppose if there is a pretxnchangegroup process hook that needs to
> access non-index data we could hit this. I would like to think we have test
> coverage of this. But something tells me most/all our tests are for
> changelogs smaller than 128kb and thus use inline data.

I did consider adding a test and test-hook.t does catch this if inline
revlog is disabled. I thought ideally with my run-tests .t multi cases
change, test-hook.t could have a new test case with inline disabled.

Since run-tests change was not ready yet but the fix is important and
straightforward, I sent it without a test.

> Yeah, that's a pretty serious bug.
> 
> I'll queue this with (API). If a queuer doesn't like the API change, we can
> work it out later.