* bf109g-yasim.xml: tweak the numbers some more. I now get realistic performance:
cruise: 320 TIAS at 6km using 1.1 ata and 2300rpm;
takeoff power: 1.4 ata, automatic pitch control yields 2600rpm;
max power is at 1.7 ata and 2800 rpm (but this will kill the engine quite quickly).
* Nasal/bf109.nas: do not control the propeller pitch or supercharger from Nasal anymore.
* Systems/engine-filters.xml: new. Control the continuously variable supercharger speed
and propeller pitch from a property rule instead of Nasal. Add automatic mixture control.
* bf109g-set.xml:
- load the above property rule.
- new key bindings: f, F to cycle the setting of radiator flaps.
- improve the help. (Take-off settings have changed: 1.4 ata and 12:00 propeller
pitch give 2600rpm and the appropriate take-off power.)
- add fallback-model-index.
