Added the ability to set the digital relays on the APM
Merge branch 'master' into enable_set_relay
Updated SLUGS message definitions to work with current version.
Allow compiling on Visual Studio 2012 and earlier.
pymavlink: closer to supporting python3
MAVExtra: Add a version of mag_field that works for Dataflash messages
MAVExtra: Teach distance_home to deal with DF GPS messages

The distance_two function that underlies distance_home already
knows how to deal with APM DF GPS messages, this patch just
has to teach distance_home about the Status field replacing
fix_type to triage the data
mavflightmodes: Print a summary of time spent in each mode.
pymavlink: extract separate missions in mavextract
pymavlink: raise version for release
pymavlink: added gains to demix functions
pymavlink: fixed X range calculation for multiple data files

this prevents the X range getting a too many ticks exception when we
are plotting multiple files with different time ranges.

Also adds --multi option to make multiple file plots not change colour
per file
pymavlink: Allow headless operation in mavgraph by providing an output file name.
ardupilotmega: merged in motor test command from ardupilot
common.xml: added MAV_CMD_DO_INVERTED_FLIGHT

used to control inverted flight in a mission
mavkml style fix
Force people to use the right header with an #error.
common.xml: Added GPS_RTK and GPS2_RTK
Add general distance sensor message
Fix message packing issues that prevent the checksum from being properly added to the packet