Use gettimeofday() and struct timevals instead of time()

Use gettimeofday() and struct timevals instead of time()

Initially I thought using the second precision time() function is good enough,
but to make t/113-urgent.t considerably faster (>2s vs. 0.08s), we put in a
little more effort and use gettimeofday. Otherwise, this test blocks the whole
testsuite from completing much faster on modern machines :).