This prohibits some nonsense like "./proxy-go -capacity -550", which
otherwise results in a panic like:
INFO: configuration.go:174: Created Configuration at &{[{[stun:stun.l.google.com:19302] }] All Balanced }
panic: makechan: size out of range
math/rand always uses a deterministic seed. The sequence of session IDs
was therefore always the same:
Uv38ByGCZU8WP18PmmIdcg
lWbHTRDYaB0NhtHpHgAWeQ
...
Multiple copies of this program would have had session ID collisions. I
don't know what the consequences of that would be.
