RFR: Add default safe methods for Repository::checkout

[Erik Duveblad via github.com]

Hi all,

this tiny patch just adds two default implementations for `Repository::checkout` that are safe to use (I got annoyed at having to add `false` to all my `checkout` calls).

Thanks,
Erik

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Commits:
 - b45957d7:	Add default safe methods for Repository::checkout

Pull request:
https://git.openjdk.java.net/skara/pull/94

Webrev:
https://webrevs.openjdk.java.net/skara/94/webrev.00

Patch:
https://git.openjdk.java.net/skara/pull/94.diff

Fetch command:
git fetch https://git.openjdk.java.net/skara pull/94/head:pull/94