largefiles: walk history in ascending order while downloading all lfiles
I don't think the order matters. Maybe it's purely because of the use of
walkchangerevs(), which was originally designed for "hg log" command.
Surprisingly, the number of objects fetched in test-largefiles.t has changed.
According to the --verbose output, the order of the following fetches flipped
and the latter got deduplicated.
getting large3:
eb7338044dc27f9bc59b8dd5a246b065ead7a9c4
found
eb7338044dc27f9bc59b8dd5a246b065ead7a9c4 in store
getting sub/large4:
eb7338044dc27f9bc59b8dd5a246b065ead7a9c4
found
eb7338044dc27f9bc59b8dd5a246b065ead7a9c4 in store