RFR: Batch commit, add and files methods in HgRepository

[Erik Duveblad via github.com]

Hi all,

this small patch adds "batching" to the `commit`, `add` and `files` methods in `HgRepository` to avoid command-line overflow for large lists.

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

Thanks,
Erik

----------------

Commits:
 - 5f2088c0:	Batch commit, add and files methods in HgRepository

Pull request:
https://git.openjdk.java.net/skara/pull/109

Webrev:
https://webrevs.openjdk.java.net/skara/109/webrev.00

Patch:
https://git.openjdk.java.net/skara/pull/109.diff

Fetch command:
git fetch https://git.openjdk.java.net/skara pull/109/head:pull/109