Removed unnecessary debugging code from mavgenerate.py
Added generation option to disable XML validation.
Useful when generating a lot of code and the XML files are known to be good, but it's still left on by default.
Extended support for disabling validation to the mavgenerate GUI.
Removed some redundant code from mavgenerate and made more code from mavgen reusable.
Corrected XML for new MAV_DISTANCE_SENSOR message
add flighttermination command
Merge pull request #219 from mavlink/flightterminationcommand

add flighttermination command
pymavlink: raise version
common.xml: added TERRAIN_* messages
pymavlink: added --condition to magfit_gps.py
pymavlink: raise version
common.xml: added MAV_SYS_STATUS_TERRAIN
common.xml: added MAV_CMD_PREFLIGHT_SET_SENSOR_OFFSETS for 2nd magnetometer
ardupilotmega.xml: merged latest changes from ardupilot git
XML: resolved conflicts between APM and PX4 MAV_CMD_* messages

as discussed with Lorenz and Randy
Fix docs in XML on quaternions
Fix conversion docs in C
common.xml: added MAV_FRAME_GLOBAL_TERRAIN_ALT
pymavlink: added support for terrain altitude mission creation
pymavlink: raise version
common.xml: added current height above the location to TERRAIN_REPORT

this is a very useful piece of information in the TERRAIN_REPORT, and
should be displayed on GCS status page
pymavlink: raise version