RFR: 11: git-skara update should only rebuild if updates are found

[Erik Duveblad via github.com]

Hi,

this small patch ensures that we only rebuild the Skara tooling during `git skara update` if the tool actually pulled down some commits.

Thanks,
Erik

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Commits:
 - 1ed20df2:	11: git-skara update should only rebuild if updates are found

Pull request:
https://github.com/openjdk/skara/pull/1

Webrev:
https://openjdk.github.io/cr/skara/1/webrev.00

Patch:
https://github.com/openjdk/skara/pull/1.diff

Fetch command:
git fetch https://github.com/openjdk/skara.git 1ed20df2:pr/1