* Nasal/bombable.nas (load(), unload()):
do not call cmdarg() from a Nasal file; take a node parameter
instead.
* Models/MiG-15bis.xml: call cmdarg() only from <load></load>
and <unload></unload> scripts embedded in the XML; pass the
node object to load() and unload().
* Models/Submodels/MiG-15bis-submodels.xml: correct the
ballistics of one of the 23-mm cannons.
