* Fix jmavsim HITL simulation of MAV_CMD_DO_REPOSITION in the case where you have no radio attached to the PX4 and so you have disabled RC link loss for that reason (set NAV_RCL_ACT = 0) but you still want the jmavsimulation to work.  The line of code changed here causes failsafe RTL to kick in without this fix.

* Add altitude hold option using Z position control, while doing velocity control on vx and vy.

* Fix style and rebase issues