This is to make sure that the server doesn't run LFC twice before
it is reconfigured.

    Fixed typos and added decline lease checks for DHCPv6

src/lib/dhcp/duid.h
src/lib/dhcp/duid.cc
src/lib/dhcp/tests/duid_unittest.cc
    - Replaced DUID::generateEmpty() with DUID::EMPTY() which returns
    a constant reference to a static DUID instance.  This facilitates
    comparisions.
    - Updated TEST(DuidTest,empty) accordingly

src/lib/dhcpsrv/csv_lease_file6.cc
    CSVLeaseFile6::next() - added test to permit the Empty DUID
    only if state is STATE_DECLINED.

src/lib/dhcpsrv/lease.cc
    Lease6::decline() - modified to use DUID::EMPTY().

src/lib/dhcpsrv/tests/csv_lease_file4_unittest.cc
    Fixed Typos

src/lib/dhcpsrv/tests/csv_lease_file6_unittest.cc
    TEST_F(CSVLeaseFile6Test, declinedLeaseTest) - new test to
    verify proper handling of declined leases

The test requires that the boost headers are included, otherwise the
test reports that gtest doesn't support XXX_TRUE() macros. This
change was okayed on jabber.

src/bin/lfc/tests/lfc_controller_unittests.cc
    Fixed test data

src/lib/dhcpsrv/dhcpsrv_messages.mes
    added new error log message DHCPSRV_MEMFILE_LEASE_LOAD_ROW_ERROR

src/lib/dhcpsrv/lease_file_loader.h
    LeaseFileLoader::load() - new emits a error log for each row that
    fails to load

src/lib/dhcpsrv/csv_lease_file4.cc
    CSVLeaseFile4::next() - modified to produce a read error
    if the hardware address is empty and the lease state
    is NOT declined.

    CSVLeaseFile4::readHWAddr() - no longer throws an exception
    if the hardware address is empty

src/lib/dhcpsrv/tests/csv_lease_file4_unittest.cc
src/lib/dhcpsrv/tests/lease_file_loader_unittest.cc
    Changed test lease data so invalid records do not
    have lease state of declined

src/lib/dhcpsrv/tests/csv_lease_file4_unittest.cc
    TEST_F(CSVLeaseFile4Test, declinedLeaseTest) - new test