BIND 10 #2499: basic post-load validation for in-memory data source

[BIND 10 Development]

#2499: basic post-load validation for in-memory data source
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            Reporter:  jinmei        |                        Owner:
                Type:  task          |                       Status:  new
            Priority:  medium        |                    Milestone:  New
           Component:  data source   |  Tasks
           Sensitive:  0             |                     Keywords:
         Sub-Project:  DNS           |              Defect Severity:  N/A
Estimated Difficulty:  0             |  Feature Depending on Ticket:
         Total Hours:  0             |  loadzone-ng
                                     |          Add Hours to Ticket:  0
                                     |                    Internal?:  0
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 Since we don't use the standard updater for in-memory we cannot use
 #2436 for it.  We need to define in-memory specific derived class
 of `RRsetCollection` and calls `validateZone()` at around the end of
 `loadZoneDataInternal()` instead of its own ad-hoc check:
 {{{#!cpp
     // When an empty zone file is loaded, the origin doesn't even have
     // an SOA RR. This condition should be avoided, and hence load()
     // should throw when an empty zone is loaded.
     if (RdataSet::find(rdataset, RRType::SOA()) == NULL) {
         isc_throw(EmptyZone,
                   "Won't create an empty zone for: " << zone_name);
     }
 }}}

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Ticket URL: <http://bind10.isc.org/ticket/2499>
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BIND 10 Development