BIND 10 #2575: implement DataSourceClient::deleteZone and its SQLite3 implementation

[BIND 10 Development]

#2575: implement DataSourceClient::deleteZone and its SQLite3 implementation
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            Reporter:  jinmei        |                        Owner:
                Type:  task          |  jinmei
            Priority:  medium        |                       Status:
           Component:  data source   |  accepted
            Keywords:                |                    Milestone:
           Sensitive:  0             |  Sprint-20130122
         Sub-Project:  DNS           |                   Resolution:
Estimated Difficulty:  3             |                 CVSS Scoring:
         Total Hours:  0             |              Defect Severity:  N/A
                                     |  Feature Depending on Ticket:
                                     |  loadzone-ng
                                     |          Add Hours to Ticket:  0
                                     |                    Internal?:  0
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Comment (by jinmei):

 trac2575 is ready for review.

 I made some piggy-back cleanups and test enhancements, but these
 should be straightforward.  I believe the main implementation and test
 are also straightforward and easy to understand, especially with
 the understanding of the addZone() interfaces.

 There's one possible discussion point in the API, though.  See the
 note for `DataSourceClient::deleteZone`.

 I don't plan to add a changelog entry as it's quite tentative and
 at the moment mostly for internal use only.  (createZone/addZone didn't
 have an entry either).

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Ticket URL: <http://bind10.isc.org/ticket/2575#comment:5>
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