bugfix-StoringNullDates

Storing a completely null date should result in a null value in the database. 
Storing time values changed to only send the time portion. Postgresql chokes on sending date info to a Time field, whereas MySql just ignores the date into.
Additional unit tests on dates too, including one to highlight this problem.
Fixing Postgresql driver issues. Fixing PostgreSql .sql file to correctly delete tables before trying to recreate tables, since Postgresql can't turn off foreign key checks and turn them back on like Mysql can.
Fixes to the PDO driver for PostgreSql too.