BIND 10 #2746: allow loading log messages manually and use it for Python datasrc

[BIND 10 Development]

#2746: allow loading log messages manually and use it for Python datasrc
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            Reporter:  jinmei        |                        Owner:
                Type:  defect        |  UnAssigned
            Priority:  medium        |                       Status:
           Component:  logging       |  reviewing
            Keywords:                |                    Milestone:
           Sensitive:  0             |  Sprint-20130305
         Sub-Project:  Core          |                   Resolution:
Estimated Difficulty:  5             |                 CVSS Scoring:
         Total Hours:  0             |              Defect Severity:  N/A
                                     |  Feature Depending on Ticket:
                                     |          Add Hours to Ticket:  0
                                     |                    Internal?:  0
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Changes (by jelte):

 * owner:  jelte => UnAssigned
 * status:  assigned => reviewing


Comment:

 The initial change was almost trivial.

 I have done a number of the additional suggestions, but not all of them.

 - getDuplicates() now returns const vector
 - added a clearDuplicates()
 - clearDuplicates is called in logger manager's init()
 - added the ignore_duplicates argument to loadDictionary()
 - added loadDictionary in sqlite3_accessor, and moved sqlite3 log messages
 to separate file

 (perhaps not exactly in that order, but I think the commit messages are
 self-explanatory)

 Things I did not do:
 - created wiki page; not sure where this would currently fit, tbh
 - I left MessageInitializer a class; most functionality can indeed just be
 functions in a namespace, however the initializer is (mis)used to call the
 constructor outside of a function right now.

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Ticket URL: <https://bind10.isc.org/ticket/2746#comment:5>
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