BIND 10 #2109: redefine in-memory zone finder (basic)

[BIND 10 Development]

#2109: redefine in-memory zone finder (basic)
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            Reporter:  jinmei        |                        Owner:
                Type:  task          |                       Status:  new
            Priority:  medium        |                    Milestone:  Next-
           Component:  data source   |  Sprint-Proposed
           Sensitive:  0             |                     Keywords:
         Sub-Project:  DNS           |              Defect Severity:  N/A
Estimated Difficulty:  0             |  Feature Depending on Ticket:
         Total Hours:  0             |  scalable inmemory
                                     |          Add Hours to Ticket:  0
                                     |                    Internal?:  0
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 With #2108, the `InMemoryZoneFinder` can now concentrate on its
 find()-related tasks.  It will be constructed with `ZoneData`,
 and will be constructed by revised `ZoneTable`.

 It will still be quite complicated, so it's probably defined in a
 separate .cc file.

 It probably makes more sense to move ZoneData::findNode() to finder's
 dedicated subroutine (in an unnamed namespace - it shouldn't have to
 be a member function of the finder).

 This task ports the basic part of its find() and findAll().  Skip
 wildcard consideration.  Also just use the base (default) result
 context.

 Depend on #2107 and #2108.

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Ticket URL: <http://bind10.isc.org/ticket/2109>
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