AP_TECS: added get_max_climbrate()
AP_SpdHgtControl: added get_max_climbrate()
AP_Math: prevent negative longitude scaling

for crazy locations
AP_Terrain: added terrain lookahead API

this allows for predicting altitude needed to climb over upcoming
terrain
Plane: added TERRAIN_LOOKAHD parameter

distance to look forward for terrain following
AP_Terrain: added note on CPU cost of height_amsl()
build: allow "make px4-v2-hil-upload"