sql/field.cc:
  initialize ltime completely
sql/filesort.cc:
  don't pack MYSQL_TIME if it's not initialized
  (safe here, but valgrind complains)
sql/item_cmpfunc.cc:
  don't pack MYSQL_TIME if it's not initialized
  (safe here, but valgrind complains)
sql/item_timefunc.cc:
  don't check MYSQL_TIME members if it's uninitialized
  (safe here, but valgrind complains)
sql/time.cc:
  use c_ptr_safe() instead of c_ptr()
  (make valgrind happy)