[SPARK-5003][SQL]cast support date data type

enable cast to support date data type
such as : 
select * from tableX where dateFiled > cast('2014-12-30' as date)
If  I don't change this, the test will fail because of the time zone problem in my local test environment.Obviously, it still has the time zone problem in spark test environment even change this, I will try to fix it :)