Quick and dirty server testing.
Properly test registration and deregistration in server throughput test script.
Fix player deregistration never finding player to deregister bug.

Was comparing by reference, rather than by value.
Fix double-ACK bug upon player deregistration bug.
Script to test a huge number of spectators to a game.
Use thread-safe collections.

Spectators is expected to be low-count, low-churn, hence the use of a
COW, array-based set, rather than a skiplist based one.
Add Javadoc.
Don't needlessly expose internal methods.