bf109: bug fix: correct manifold pressure indication
* Models/Instruments/man18-ger/man18-ger.xml: The manifold pressure was underestimated; if you tried to respect the limits in the help, you used less power than the engine could deliver. Rewrite the interpolation for the needle.
Authored by: lbrenta 2018-10-10
Parent: [r3594]
Child: [r3596]
