The isc_time_add() and isc_time_subtract() didn't have a unit test, add
the unit test with couple of edge case vectors to check whether overflow
and underflow is correctly handled.
(cherry picked from commit 04511736a0)
The isc_time_add() and isc_time_subtract() didn't have a unit test, add
the unit test with couple of edge case vectors to check whether overflow
and underflow is correctly handled.
(cherry picked from commit 04511736a0)