Added logging.c as a source to libdb.la in tests/unit

Because all mutex locking/unlocking now require Log(). This caused a
bunch of changes like renaming libdb.la intermediate objects (by
redefining libdb_la_CPPFLAGS) and removing lots of logging stubs from
various tests.
Fix db_load test double symbols during linking.
Merge pull request #1620 from jimis/agent_protocol_version

Added logging.c as a source to libdb.la in tests/unit