Record into ~unitproc/bkFreqWrite~ how ~bklog~ writes stdin to disk in
regularly timed intervals (using a conditional ~while~ loop). See
EVA-2020-02 for a copy of ~bklog~.
+*** 2021-01-26: Replace ~echoerr~ with ~yell~ in ~bktemplate~
+~yell~ is shorter to call than ~echoerr~.