BIND 10 #1607: define ZoneFinder::findAdditional() and implement its default version

[BIND 10 Development]

#1607: define ZoneFinder::findAdditional() and implement its default version
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            Reporter:  jinmei        |                        Owner:
                Type:  defect        |                       Status:  new
            Priority:  major         |                    Milestone:  Year
           Component:  b10-auth      |  3 Task Backlog
           Sensitive:  0             |                     Keywords:
         Sub-Project:  DNS           |              Defect Severity:  N/A
Estimated Difficulty:  0             |  Feature Depending on Ticket:  auth
         Total Hours:  0             |  performance
                                     |          Add Hours to Ticket:  0
                                     |                    Internal?:  0
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 This is a subtask for "Pre-establish shortcuts for additional section
 processing" described in
 https://lists.isc.org/pipermail/bind10-dev/2012-January/002985.html

 We add a new method `findAdditional()` to the `ZoneFinder` class.  It
 would look like as follows:

 {{{#!c++
 void
 ZoneFinder::findAdditional(const isc::dns::AbstractRRset& rrset,
                            const std::vector<isc::dns::RRType>&
 requested_types,
                            std::vector<isc::dns::ConstRRsetPtr>& result,
                            FindOptions options);
 }}}

 We provide the default implementation of it.  The default version
 behaves `Query::addAdditional()` and `Query::addAdditionalAddrs()`
 currently do.  `Query::addAdditional()` will now just call
 the new method.  requested_types stores the desired RR types to be
 returned as associated (additional) data for rrset.  In practice
 it will be either or both of A and AAAA.  findAdditional() returns any
 found RRsets in the result variable.  In options we can specify
 whether glue is okay or not.

 With this update `Query::addAdditionalAddrs()` will become unnecessary
 so should be removed.

-- 
Ticket URL: <http://bind10.isc.org/ticket/1607>
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