[11] update datasrc clients mgr to handle configured generation IDs.
[11] updated ddns so it'll include configured datasrc gen ID to other modules.
[11] refactoring: update xfrin internal so datasrc genID is retrieved

also made straightforward adjustment to tests.  genID isn't used yet.
[11] revised post-xfrin notification so it'll include datasrc gen ID.

adjusted tests accordingly.  also, re-enable TestXfrinProcessCloseCheck
(renamed from TestXfrinProcess, which was accidentally overridden by
another definition of the same class name and disabled as a result).
[11] added a log message on data source reconfiguration, added test case for it.
[11] adjusted a few more tests for the gen ID support in datasrc configuration.

(previously just overlooked; now all tests passed).
Merge pull request #12 from bundy-dns/issue11

Issue11: update ddns and xfrin to support data source generation ID