Fixed typo, improved logging, removed unused type parameter.
Introduced factory method to create the SelectorManager instance.
Introduced field "submitKeyUpdates" instead of relying on a system
property.

Modified method updateKey() to return a boolean to signal whether the
selector was woken up.
443713 - Reduce number of SelectionKey.setInterestOps() calls.

Introduced a state machine to handle the various scenarios (ST = selector thread, Tx = pooled thread):

ST: call to SCEP.onSelected() moves from SELECTING -> PENDING.
ST: call to SCEP.updateKey() moves from PENDING -> UPDATING -> SELECTING
T1: call to SCEP.changeInterests() moves (SELECTING | PENDING) -> CHANGING -> SELECTING

The race between ST and T1 to move from PENDING to either UPDATING or CHANGING will be won
by one thread only, which will then perform the call to SelectionKey.setInterestOps().
Preferably, this will be done by ST during an updateKey() call. If updateKey() has already
been invoked, then changeInterests() will perform the call to SelectionKey.setInterestOps().

However, if T1 loses, it still has to perform the key update, so it will spin until ST
moves back to SELECTING.