Replace some "FALLTHRU" comments with control flow.

Replace some "FALLTHRU" comments with control flow.

Instead of a case statement falling through, with a "FALLTHRU" comment,
to the follow case that just does a break, continue, goto, etc.,
control-flow statement, duplicate the statement in place of the comment.
Fall-through should be the exception, and saving a break statement
doesn't offset the cognitive cost when reading the source.