Bertrand Coconnier: bug fix for #184, JSBSim: command line arguments

Bertrand Coconnier: bug fix for #184, JSBSim: command line arguments
1. The atmospheric properties of FG are not yet initialized when
JSBSim is initialized.
-> patch is quite basic and there may exist smarter ways to initialize
properly the environment before the FDM.
2. The Euler angles were initialized after the velocities.
3. The glide slope and rate of climb were ignored. Fixes all FDMs (YASim,
UIUC, JSBSim, etc.)
4. Some properties were instructed to re-use their previous value while
they should not.
5. Some bugs existed in JSBSim trim code. -> This bug has already been
fixed in JSBSim but the corresponding patch has not yet been applied to FG.