BIND 10 #1697: extend MessageRenderer so we can replace the output buffer

[BIND 10 Development]

#1697: extend MessageRenderer so we can replace the output buffer
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                   Reporter:         |                 Owner:  jinmei
  jinmei                             |                Status:  accepted
                       Type:  task   |             Milestone:
                   Priority:  major  |  Sprint-20120306
                  Component:         |            Resolution:
  libdns++                           |             Sensitive:  0
                   Keywords:         |           Sub-Project:  DNS
            Defect Severity:  N/A    |  Estimated Difficulty:  9
Feature Depending on Ticket:  auth   |           Total Hours:  0
  performance                        |
        Add Hours to Ticket:  0      |
                  Internal?:  0      |
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Comment (by jinmei):

 trac1697 is ready for review.

 The diff may look big (many files are modified), but most of the
 changes should be straightforward adjustment due to the main interface
 change.

 - the first commit (464cada) introduces one substantial change to the
   constructor and many libdns++ tests needed to be adjusted.  Maybe
   this commit should be reviewed separately.
 - fb9060e to 89f1ae8 are the main change.  4085d32 is documentation
   update for it.
 - 462e280 is changes to applications that use the renderer.  many
   files were updated, but the point of the change should be
   straightforward.

 In 462e280, I sometimes made sure the renderer buffer is reset by
 calling `setBuffer(NULL)`, and in other cases I simply let the
 renderer destructed with the specified buffer.  In the former case I
 expect we'll soon make further changes to reuse the renderer (e.g.,
 for b10-auth), and at that point resetting the buffer will be safer.
 So I did it from the beginning.

 It's a mostly internal change that almost no user will notice, but
 it's still a change to the public API, so I think we need a changelog
 entry:
 {{{
 385.?   [func]*         jinmei
         libdns++: revised the (Abstract)MessageRenderer class so that it
         has a default internal buffer and the buffer can be temporarily
         switched.  The constructor interface was modified, and a new
         method setBuffer() was added.
         (Trac #1697, git TBD)
 }}}

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Ticket URL: <http://bind10.isc.org/ticket/1697#comment:4>
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