PID counter in processserver can overflow

[eikendev]

We currently set num_proc in the server's state to 0 initially, and increment for each process that is registered.

We should handle overflows, so the same PID cannot be assigned to two different processes. Instead of incrementing once only, we could increment until the first "free" PID is reached, i.e., num_proc is not currently used for any other dispatcher that is still alive.