(date) as empty  string": preserve time type (date, time, or datetime) for
zero dates, times, and datetimes.


libmysql/libmysql.c:
  A fix for bug#6058 "Prepared statements return '0000-00-00' (date) as empty
   string": preserve time type (date, time, or datetime) for zero 
  dates, times, and datetimes.
tests/client_test.c:
  A test case for Bug#6058, the existing tests required some adjustments too.