Default commit/abort and prepareForAbort

[Alejandro Revilla]

Copying here the commit message

https://github.com/jpos/jPOS/commit/3f938078bbb2e9bf4df46e1d23e39469a2ad1ac1

We see a lot of transaction implementations having to override commit and rollback just to honor the API. Same happens for participants that want to get engaged at abort time so they need to implement AbortParticipant, but the prepareForAbort implementation just calls prepare.

We now provide default implementations for those.

will be available on next nightly build.

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@apr