[4275] Postgresql schema 3.0 now matches MySql schema 4.2

[4275] Postgresql schema 3.0 now matches MySql schema 4.2

Added 4.1 to 4.2 updates from MySQL and created upgrade
script for 2.0 to 3.0

src/share/database/scripts/pgsql/dhcpdb_create.pgsql
    - Enclosed the entire script in a single transaction
    - Removed DROP TABLE statements
    - Added host_identifier_type table and data
    - Added dhcp_option_scope table and data
    - Updated unqiue constraints for hosts table
    - Added scope_id and foreign key constraint to dhcp4_options table
    - Added scope_id and foreign key constraint to dhcp6_options table
    - Added unique contraint to ipv6_reservations table
    - Changed 'HWADDR_SOURCE_DOCSIS' to 'HWADDR_SOURCE_DOCSIS_CMTS'
    - Inserted row for 'HWADDR_SOURCE_UKNOWN'

src/share/database/scripts/pgsql/dhcpdb_drop.pgsql
    Added drops for host_identifier_type and  dhcp_option_scope

src/share/database/scripts/pgsql/upgrade_2.0_to_3.0.sh.in
    New file for upgrading Postgresql from 2.0 to 3.0

configure.ac
    Added src/share/database/scripts/pgsql/upgrade_2.0_to_3.0.sh

src/bin/admin/tests/pgsql_tests.sh.in
    - pgsql_upgrade_1_0_to_2_0 - new function which contains all the checks used
    to verify 1.0 to 2.0 upgrade (extracted from pgsql_upgrade_test)
    - pgsql_upgrade_2_0_to_3_0 - new function which contains all the checks used
    to verify 2.0 to 3.0 upgrade
    - pgsql_upgrade_test() - modified use new upgrade check fucntions

src/share/database/scripts/pgsql/Makefile.am
    Added entry for upgrade_2.0_to_3.0.sh