fix to use ins_alt_dot with baro wen USE_BAROMETER is defined
[modules] baro_board: only call event handler if there is new data
[modules] fix warning in baro_board
[modules] BARO_x_DT from generated BARO_x_PERIODIC_PERIOD
Merge pull request #511 from paparazzi/ins_alt_float_baro

fixes to use ins_alt_dot from ins_alt_float (with USE_BAROMETER)