Fix for human-controlled bot spam.

Mutes/bans bots used by a human player to send lots of identical
messages using different accounts while varying the message and limiting
message speed to work around anti-spam measures.
Stopped limiting tree growth.

This is a performance enhancement - the cost of limiting tree growth is
way too high considering the VERY low risk of "tree grief".  Also a
positive side effect - no more weird-looking "sliced" trees.
Better boot logging and performance.

Improved boot logs to get more specific performance numbers, and
eliminated some non-essential boot steps to improve performance.
Letting Java decide when to collect garbage.
Version to 8.1.5