RFR: webrev: do not use follow for ranges with merges

[Robin Westberg]

On Thu, 3 Sep 2020 08:05:08 GMT, Erik Helin <ehelin at openjdk.org> wrote:

> Hi all,
> 
> please review this patch that makes JSON webrev use plain `git log` if the range of commits include a merge commits.
> This is needed because `git log -c --follow` can be extremely slow for commit ranges with a lot of merge commits.
> Testing:
> - `make test` on Linux x64
> - Manual verification of performance
> 
> Thanks,
> Erik

Looks good!

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Marked as reviewed by rwestberg (Reviewer).

PR: https://git.openjdk.java.net/skara/pull/764