Reset date fields to UNIX epoch in TimeType.

TimeType resets date fields (i.e. unused DateTime object fields) to UNIX
epoch (1970-01-01). This makes TIME field mapping stabe (i.e. same time
will be always mapped to the same DateTime fields).

See DDC-179 (similar issue with DateType). Fixes DBAL-993.
Merge pull request #697 from orchitech/DBAL-993

Reset date fields to UNIX epoch in TimeType.