instead of having it hard-coded. Previous behavior caused focus to go all out
of whack if you ever changed the near/far plane (and even the default hard-coded
value was not the same as JME's default camera setup.)
While I was here, I made the unfocus threshold configurable and added a debug
toggle that will turn the 'unfocus' amount into grayscale color for better visualizing
where unfocusing is happening.
81667f8f45