BIND 10 #2098: Define and Implement `TreeNodeRRset` class

[BIND 10 Development]

#2098: Define and Implement `TreeNodeRRset` class
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                   Reporter:         |                 Owner:  jinmei
  jinmei                             |                Status:  accepted
                       Type:  task   |             Milestone:
                   Priority:         |  Sprint-20120904
  medium                             |            Resolution:
                  Component:  data   |             Sensitive:  0
  source                             |           Sub-Project:  DNS
                   Keywords:         |  Estimated Difficulty:  6
            Defect Severity:  N/A    |           Total Hours:  0
Feature Depending on Ticket:         |
  scalable inmemory                  |
        Add Hours to Ticket:  0      |
                  Internal?:  0      |
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Comment (by jinmei):

 trac2098 is ready for review.

 I rebased the branch on to a more recent version of master in the
 middle of the development, but I believe the branch tree is clean.
 (Just in case it's necessary) the effective branch point is 949291a.

 I needed to do a couple of preparation changes:
 - move the label sequence version of messagerenderer toWire() to the
   base class (b350749)
 - port getAbsoluteLabels() from the rbtree class to doamintree
   (068ecfa).
 I believe these should be a straightforward copy-and-adjust.

 Other than these, this branch essentially consists of newly introduced
 files: treenode_rrset.h, .cc, and their tests.  I'm afraid the code
 size is a bit large, but I believe the implementation is pretty easy
 to understand (even if some specific way of it may be subject to
 discussions).

 Finally, I added a simple small benchmark test under benchmarks.  I
 think it's only needed a lightweight review, or, if the branch looks
 already too big, I'm okay with excluding it for now.

-- 
Ticket URL: <https://bind10.isc.org/ticket/2098#comment:9>
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