RFR: Add ReadOnlyRepository::dump

[Erik Duveblad via github.com]

Hi all,

this patch adds the `ReadOnlyRepository::dump` method and a corresponding unit test.

## Testing
- [x] `sh gradlew test` passes on Linux x86_64

Thanks!
Erik

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Commits:
 - 6057ad07:	Add ReadOnlyRepository::dump

Pull request:
https://git.openjdk.java.net/skara/pull/78

Webrev:
https://webrevs.openjdk.java.net/skara/78/webrev.00

Patch:
https://git.openjdk.java.net/skara/pull/78.diff

Fetch command:
git fetch https://git.openjdk.java.net/skara pull/78/head:pull/78