Fixes to add default Vcc logging to dataflash

Hi,

Please review these changes to add support for default Vcc logging and battery logging to the data flash. Tested on ArduCopter master, not on ArduPlane and APMRover but I have attempted the changes, which compile.

This change will benefit support as you will be able to see if power problems are the issue.

Fixes: https://github.com/diydrones/ardupilot/issues/210

Thanks :)