redmine6476: Aborting on low entropy is too drastic.

Rather than reverting the whole commit involved, keep what we can of
it and Log() instead of UnexpectedError(), at least until Jimis can
invent some better way to respond to this.
Merge pull request #1888 from ediosyncratic/rand-fix

redmine6476: Aborting on low entropy is too drastic.

Failed automatic test, but Matthew says it's only expected failures.