RFR: vcs: make follow work with merge commits

[Robin Westberg]

On Sat, 29 Aug 2020 11:57:21 GMT, Erik Helin <ehelin at openjdk.org> wrote:

> Hi all,
> 
> please review this patch that makes `ReadOnlyRepository.follow` work with merge commits for Git repositories. I also
> added an additional unit test to verify the functionality.
> Testing:
> - [x] `make test` passes on Linux x64
> - [x] Added a new unit test
> 
> Thanks,
> Erik

Looks good!

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Marked as reviewed by rwestberg (Reviewer).

PR: https://git.openjdk.java.net/skara/pull/752