Linux/Housekeeping/Bug fixes/Extend xTreme/Defs

Another attempt to reach Linux portability: Thank you, Jim Ablett!
Housekeeping: Defined parameters that used to be typed in as numbers in
several places.
Bug fixes: Fixed several minor inconsistencies found during
housekeeping.
Extended xTreme configurability: Allowed split depths down to 8.
Other default setting changes: Alchemy; Set to "aggressive" personality
to try.
Version change: From 2.2.3 to 2.3, preemptively, in anticipation of
release thereof.