[MERGE] optimize annotate

[Aaron Bentley]

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Wouter van Heyst wrote:
> Even though the sizable amount of annotations is listified first.
> I have trouble seeing when that would become a problem, as so often with
> these kind of tradeoffs.

Knits are delta compressed, so each text 'version' must be built from
older revisions, up to the last fulltext.  If any of the intermediate
versions would be useful in generating another needed version, it's more
efficient to generate both versions at once.  So retrieving multiple
versions of the revision knit at the same time is generally faster than
retrieving the same revisions in multiple steps.

There's also disk-caching advantages.

Retrieving multiple revisions at once is the same strategy I used to
speed up 'log'.  It applies to revision_trees also.

Plus, my code avoids retrieving the same revision twice, which the old
code did not do.

Aaron
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