mwp inav 8605091 2016 03 25

inav testing branch (860509, 2016-03-25) Note how well it copes on legs WP11 to WP 12 where this is a short gap in GPS data, and on WP12 to WP13 where the sat count drops to 4 and HDOP goes from the average of around 1.5 to greater than 8. Boringly awesome, and getting lazy (shall I land this machine or just hit RTH and let inav do the landing :-)