Almost final removal of the get_date() and get_time() methods in Item_field, Field and Item_func classes.
Removal of obselete synonym variants of NOW() function from parser as well as additional non-valid variants of NOW(expr) and SYSDATE(expr)
Fixed up the Item_date_typecast, Item_datetime_typecast, and Item_time_typecase Items
Added Temporal derived-specific store() methods in Protocol.
Ensured all Field classes which dealt with Temporal values were as efficient in storing and retrieving temporal values as possible.
The Temporal classes are now only a few steps from being true ValueObjects.
I need to code through the last remaining operator overloads and make the classes Immutable. After that, they may serve as a model for future work on ValueObjects.