Windows has a low resolution timer.
Some of the tests assumed that unblock takes effect immediately.
Consider:
t := time.Now()
elapsed := time.Now().After(t)
It seems plausible that elapsed should always be true.
However, with a low resolution timer, that might fail.
Change time.Now().After to !time.Now().Before,
so that unblocking always takes effect immediately.
Fixes#873.
7c1a9e8616