mavlink: use altitude AMSL in VFR message
Merge branch 'master' into vfr_fix
Merge pull request #1391 from PX4/vfr_fix

mavlink: use altitude AMSL in VFR message
Fix vehicle command docs to AMSL
uORB mission topic: Add AMSL as clarificaiton in docs
uORB home position: Add AMSL as clarificaiton in docs
Merge remote-tracking branch 'upstream/master' into d3_second_try