Update jsbsim to the current trunk & make compile on mavericks.

This should be tested on older OSX before being merged. I tried to compile nps using the newer version of jsbsim and it definitely needs updating. PropertyManager vs. PropertyNode classes got restructured a bit. I do not understand enough about the simulation stuff to confidently update nps code to the newer version of jsbsim so I would appreciated some help with that. :)