The default setting for only_ways was [], which meant "all ways".
However, it's really useful to have [] mean "no ways".

In cgrun057 I used only_ways(prof_ways) to mean "only run this in the
profiling ways", but if profiling is disabled then prof_ways = [] and
this doesn't do what we want.  Profiling is normally disabled in
validate, but I had it enabled because I was testing profiling.

So now only_ways defaults to None, which means "all ways", and [] now
means "no ways".