Implemented wxSingleInstanceChecker to only allow one instance of OFF
to run per userID.

CRITICAL: fixed overflow/NULL-termination crashers related to ludicrously
long usernames. In previous versions, someone could crash your node by
sending an overly long username - upgrade strongly recommended.

Limited username display in chat to 24 chars for readability.

Async read objects no longer need to create a copy of a node object.

Fixed bug where a blocks request count could get incremented when
no request was actually made.