Vladislav Zavialov authored Feb 25, 2019 and Ben Gamari committed Jun 24, 2019

We use "touch -r" to set modification timestamps, which leads to precision loss
on Darwin. For example,

   before: 2019-02-25 01:11:23.807627350 +0300
   after:  2019-02-25 01:11:23.807627000 +0300
                                     ^^^
This means we can't trick GHCi into thinking the file hasn't been changed by
restoring its old timestamp, as we cannot faithfully restore all digits.

The solution is to nullify the insignificant digits before the first :load

(cherry picked from commit f320f3b2)