MiG-15bis v3.1.19: Three minor edits and one bugfix (thanks to engblom on irc.flightgear.org!)
* Nasal bugfix (gui font option).
* When the gunsight is disabled, there is still ammunition (otherwise
the CoG is too far back).
* The menu option "Refuel aircraft" also refills ammunition.
* Minor help text edit.
