RFR: Fix implementation of addremove

[Erik Duveblad via github.com]

Hi,

this patch fix the implementation of `Repository::addremove` to use the proper underlying VCS primitives.

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

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Commits:
 - e3631353:	Fix implementation of addremove

Pull request:
https://git.openjdk.java.net/skara/pull/47

Webrev:
https://webrevs.openjdk.java.net/skara/47/webrev.00

Patch:
https://git.openjdk.java.net/skara/pull/47.diff

Fetch command:
git fetch https://git.openjdk.java.net/skara pull/47/head:pull/47