src/lib/dhcpsrv/pgsql_lease_mgr.h
src/lib/dhcpsrv/pgsql_lease_mgr.cc
        Replaced this class heirarchy:
        AddressStatsQuery4 <-- PgSqlAddressStatsQuery4
        AddressStatsQuery6 <-- PgSqlAddressStatsQuery6

        With this one:
        LeaseStatsQuery <-- PgSqlLeaseStatsQuery