sleep for 0.05 seconds instead of 2 seconds when checking if the pids
are still alive for a much faster exit.
Add local parsecheck() function and use it for several tests.

Instead of just checking that parsedate(3) does not return an error,
also pass the result through localtime_r(3) or gmtime_r(3) and check the
year/month/day/hour/minute/second fields in the resulting struct tm.
Add comments for some non-obvious cases.
Also add a test with year=70, which is documented to be treated as 1970.