src/share/database/scripts/pgsql/dhcpdb_create.pgsql
    Adds lease<4/6>_stat tables and triggers
src/share/database/scripts/pgsql/dhcpdb_drop.pgsql
    Added drops for lease<4/6>_stat tables and triggers

src/share/database/scripts/pgsql/upgrade_3.3_to_4.0.sh.in
    Adds lease<4/6>_stat tables and triggers
    Populates stat tables from existing lease table content
src/bin/admin/tests/mysql_tests.sh.in
    mysql_lease6_stat_per_type() - fixed typo in test

src/bin/admin/tests/pgsql_tests.sh.in
    run_statement() - new convenience fucntion for
    running statement with option expected outcome

    pgsql_upgrade_schema_to_version() - new function
    which converts the existing schema to a target version

    pgsql_lease4_stat_test() - tests v4 stat table and
    triggers in an new database

    pgsql_lease6_stat_test() - tests v6 stat table and
    triggers in an new database.

    pgsql_lease6_stat_per_type() - helper function which
    tests v6 stat table and triggers using a given address
    and lease type

    pgsql_lease_stat_upgrade_test() - tests data migration,
    stat table and trigger operations on an upgraded database

src/lib/dhcpsrv/pgsql_lease_mgr.*
    Added new SQL statements for lease stats queries

    PgSqlLeaseStatsQuery
        Constructors - added variants to support where clause params
        start() - modified to support query variants based
        on where clause params

    PgSqlLeaseMgr
        Added start variants:
        - startSubnetLeaseStatsQuery4(const SubnetID& subnet_id)
        - startSubnetRangeLeaseStatsQuery4(const SubnetID& first_subnet_id,
                                         const SubnetID& last_subnet_id)

src/lib/dhcpsrv/tests/pgsql_lease_mgr_unittest.cc
    New unit tests:
    - TEST_F(PgSqlLeaseMgrTest, leaseStatsQuery4)
    - TEST_F(PgSqlLeaseMgrTest, leaseStatsQuery6)