JSBSim syncing. The changelog is:

JSBSim syncing. The changelog is:
* The Pitot angle can now be tweaked with the <pitot_angle> tag in the <metrics> block.
* The refuel rate is now configurable with the <refuel-rate> tag in the <propulsion> block.
* Fixed C++11 compliance. JSBSim can now be compiled with a C++11 compiler.
* Avoid a spurious mass report to be issued when resetting.
* Fixed the moments computation. Previously they were computed with the previous time step CG position.
* Fixed a bug where the CG update was delayed to the next time step when point masses location were modified via the FCS.