RFR: git-sync: add --fast-forward option

[Robin Westberg]

On Wed, 11 Dec 2019 08:44:26 GMT, Erik Helin <ehelin at openjdk.org> wrote:

> Hi all,
> 
> please review this patch that adds the `--fast-forward` option to `git-sync`.
> Setting the option `--fast-forward` will cause `git-sync` to fast-forward all
> local branches where possible. Since it is mostly common that developer's do
> not make change to branches in their personal forks that are also present in
> the upstream repository, the effect is that all local branches that map to
> upstream branches (via the personal fork) will be updated locally.
> 
> Thanks,
> Erik
> 
> - Manual testing of `git-sync` on Linux x64

Looks good!

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Marked as reviewed by rwestberg (Reviewer).

PR: https://git.openjdk.java.net/skara/pull/309