Set PLACK_RESTARTER_PID?

[miyagawa]

throughnothing/Ubic-Service-Starman@d7bfc03#commitcomment-1238187

It's a known issue that some PSGI handlers such as Starman do not work as expected if you run it with plackup and -r option. Would it make sense to set some environment variable in Restarter before executing the child handler, so that the child can detect if it's running supervised, and gives warnings or throws exceptions if necessary?