When we made assertions not get compiled in for the coverage case, we
missed one case where, for our tests, we really DO want to have an
assertion fail: the backtrace test.
Bugfix on 1228dd293b60a8eaab03472fa29428c5e2752c44; bug not in any
released tor
(And replay them once we know our first real logs.)
This is an implementation for issue 6938. It solves the problem of
early log mesages not getting sent to log files, but not the issue of
early log messages not getting sent to controllers.
