[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)
This might be clearer as

```scala
Row(java.sql.Date.valueOf("2012-02-12")) :: 
Row(java.sql.Date.valueOf("2013-03-13")) :: Nil
```