Railmail broken in 1.1.6?

With the security update for 1.1.6, it seems the routing changes has
affected railmail – now I’m getting a routing error for /railmail/,
which is supplied by the plugin itself.

I know that the opportunistic/greedy loading of .rb files has been tuned
down, which is probably causing the problem, but I have no idea how to
fix this, or to tell rails to mix in controllers from
vendor/plugins/railmail/ again.

Any tips?