added setting of 'neg' in Item_param::set_time() (looks like the only forgotten
member).
It's the second place I find where 'neg' was forgotten.
The symptom was unexpected negative times in the binary log when running
tests/client_test.c (test_date() in fact):
# at 43009
#040210 15:46:42 server id 1  log_pos 43009     Query   thread_id=1     exec_time=0     error_code=0
SET TIMESTAMP=1076424402;
INSERT INTO test_date VALUES('2000-01-10 11:16:20','-11:16:20' etc