AC_PosControl: bug fix dt calculation

fixes issue in which now could be earlier than _last_update_xy_ms
leading to a large dt value and a sudden lean on takeoff
Added name to GIT_Success.txt
Copter: fix compiler warning in control_auto.pde
Copter: minor format fix
Copter: minor formatting fix
Copter: fix compiler warnings in GCS_Mavlink.pde
AP_NavEKF: Track baro alt when pre-armed

This will help prevent spurious alt disparity warning messages for copter