BIND 10 #1206: Create datasource factory

[BIND 10 Development]

#1206: Create datasource factory
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                   Reporter:         |                 Owner:  UnAssigned
  stephen                            |                Status:  reviewing
                       Type:  task   |             Milestone:
                   Priority:  major  |  Sprint-20110927
                  Component:  data   |            Resolution:
  source                             |             Sensitive:  0
                   Keywords:         |           Sub-Project:  DNS
            Defect Severity:  N/A    |  Estimated Difficulty:  4
Feature Depending on Ticket:         |           Total Hours:  0
        Add Hours to Ticket:  0      |
                  Internal?:  0      |
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Changes (by jelte):

 * owner:  jelte => UnAssigned
 * status:  assigned => reviewing


Comment:

 Ok, so I've made it into a DataSourceClientContainer class, which serves
 as both a factory and a container; it autoloads (and clears) a dlopened
 library (through a LibraryHolder class for RAII), then initialized it
 through 'factory' functions with a fixed name implemented by the various
 libraries, and cleans up through a destructor provided by those libs as
 well.

 See documentation i added in client.h and factory.h

 Because memory is still directly used by auth and some other stuff i did
 have to put in a few temporary tweaks to their makefiles.

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Ticket URL: <http://bind10.isc.org/ticket/1206#comment:7>
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