BIND 10 #2093: implement RBNode Node::getAbsoluteLabelSequence

[BIND 10 Development]

#2093: implement RBNode Node::getAbsoluteLabelSequence
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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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 This returns a LabelSequence object corresponding to the absolute name
 of the node.  Since the node itself may not be absolute, it generally
 needs to use the newly introduced "getUpLevelNode()" method.  We'll
 need this for message rendering, so it should be efficient as well as
 safe.  In my experiment I'll let the call pass sufficient size of
 buffers for name and offset data, and have the method fill in the
 buffer, and then construct the LabelSequence.  Assuming the buffers
 can be reasonably reused this is probably okay in terms of efficiency,
 but may not be very safe.  we may want to introduce an extension to
 LabelSequence so keep its user as agnostic as possible about its
 internal.

 On top of this, I also suggest adding Node::getAbsoluteName()
 method.  It calls getAbsoluteLabelSequence and construct a name
 object and returns it.  It's inefficient, but will be more
 convenient for things like debug logging.

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Ticket URL: <http://bind10.isc.org/ticket/2093>
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