Debug: fixes for Nuttx.py debug gdb add-ons

also fixed preceding mask calculation in show heaps
Debug: fixes for gdb extension macros
tone_alarm: add PARACHUTE_RELEASE_TUNE
px4io: support PX4IO_P_SETUP_FORCE_SAFETY_OFF

this allows the FMU to force the safety off on the IO board. Useful in
two cases:

 1) vehicles where the safety switch is impractical or not useful
 (eg. HAB planes or internal combustion motors)

 2) doing ESC calibration on multi-copters
pwm: added PWM_SERVO_SET_FORCE_SAFETY_OFF ioctl

this allows the safety switch on px4io to be forced off
add options do disable or fake gps output in rcS
remove whitespace
mc_pos_control: hotfix, MPC_TILTMAX_AIR and MPC_TILTMAX_LND parameters fixed
Merge pull request #875 from PX4/gpsflag

rcS: add options to disable or fake gps output