Backport some JSBProp branch changes

Add a getter for thrustTransforms to engine wrapper; change exhaust
thrust to be pressure-based, not speed-based; add a volumetric
efficiency tweak (can be disabled by setting guiactive=false) so you can
tweak an engine's HP. Also turn off engine response time (in case it was
ever on)., tweak the HP2W constant for accuracy, comment some unused
code, and fix a copy-paste typo with boost autoswitch.
update dll for those changes (note: dev FAR)