[gps] add support for Piksi gps from Swift-Nav (#957)
fix code style
[piksi] handle msl/geoid alt
Merge pull request #1043 from paparazzi/piksi

[gps] add support for Piksi gps from Swift-Nav

closes #957
[fix] re-added brackets for correct transition offset handling
Spelling correction
[linux] handle SIGINT by hand if needed, useful for debug

type Ctrl-C two to stop the program launched from the console on
ardrone2 and bebop

close #1008
third release candidate for next stable release v5.4