Log_Write_Baro should be an empty function when logging is disabled
Fix contributed by Jason Short

Based on original work by Nils Hogberg

Based on original work by Nils Hogberg

Based on original work by Nils Hogberg

Based on original work by Nils Hogberg

Based on original work by Nils Hogberg

Modified and integrated by Randy Mackay

Based on original work by Nils Hogberg

DisplayName isn't a description

this prevents us setting trim values under joystick control

- added MIS_AUTORESTART parameter, defaults to 0
- added start_or_resume() function to either start or resume a mission
based on that parameter value

Resolves issue #435
If the altitude fence is enabled, when the vehicle RTLs it will return
at the lower of the RTL_ALT and the FENCE_ALT_MAX

This resolves issue #880 in which if a GPS failsafe occurred while the
vehicle was already in LAND mode, the LAND would continue to be GPS
controlled LAND instead of pilot-controlled LAND

saves 2 bytes

This resolves issue #461 by giving the pilot a minimum of 10 seconds to
attempt to manually recover before the autopilot will attempt to retake
control to bring the copter home or land.

This ensures invalid pilot desired accelerations are cleared from the
loiter controller.  This is probably not strictly necessary because the
vehicle should switch out of Loiter and into RTL during failsafe.

Resolves issue in which vehicle would get stuck at RTL_ALT_FINAL if
failsafe occured.
Also clear out pilot acceleration from loiter controller if failsafe
occurs during the final descent.

This allows quickly clearing out the pilot desired acceleration for
loiter contoller.