- DataSource renamed to DatabaseConnection
 - exception now prints missing parameter name
 - description updated
 - unnecessary this removed

 - code refactoring after last commit, clean-up, compilation fixes
 - Makefile updates
 - Added new unit-tests for DataSource (mostly moved from LeaseMgr
   unit-tests)

Comments have been improved in one file.  The other contains a test
that alters logging, so a test fixture has been added that ressets
the logging back to the default in its destructor.

Some unit tests in dhcpsrv altered the logging configuration but
never reset it. That configuration was then used for subsequent
tests and made them overly verbose.

This is now constructed "ont the fly" when the configuration change
is committed.

Also add ability to handle incremental changes.

Able to construct a database access string from elements in the
configuration database.  No semantic checks have been done yet.