PumaWorkerKiller is used for periodically checking and killing
workers (the biggest one) if overall memory reaches specified
limit. This metric allows us to watch number of killed workers.
The Puma Worker Killer checks the total RAM used by both the master
and worker processes. Bump the limits to N+1 instead of N workers
to account for this.
This allows us (and others) to test drive Puma without it affecting all
users. Puma can be enabled by setting the environment variable
"EXPERIMENTAL_PUMA" to a non empty value.