Changing data types for:
- seconds from longlong to ulonglong
- microseconds from long to ulong
in:
- parameters of calc_time_diff()
- parameters of calc_time_from_sec()
- Members of Sec6_add

This will help to reuse the code easier:
all other functions use ulonglong+long
for seconds/microsecond, e.g.:

- number_to_time()
- number_to_datetime()
- number_to_datetime_with_warn()
- Field_temporal_with_date::store_decimal()
- my_decimal2seconds()
- Item::get_seconds()