Added extensions needed for porting PX4 to BeagleBone Blue; Made it compatible with PX4 build environment: resolved float number comparison issue, renamed global variable names to avoid collisions, etc.

0.4.1 git20180424 systemd generic board fixes

Just exit cleanly when rc_model doesn't match grep of /boot/uEnv.txt

Fixes:
systemd[1]: Started rc_battery_monitor.
rc_battery_monitor[1134]: rc_battery_monitor can only run on BB Blue, Black, and Black wireless when the roboticscape device tree is in use.
systemd[1]: rc_battery_monitor.service: Main process exited, code=exited, status=255/n/a
systemd[1]: rc_battery_monitor.service: Failed with result 'exit-code'.

Signed-off-by: Robert Nelson <robertcnelson@gmail.com>

ExecStart, add the conditional '-' option to encase /etc/roboticscape/link_to_startup_program was never created.

Fixes:

systemd[1]: Started roboticscape.
systemd[951]: roboticscape.service: Failed to execute command: No such file or directory
systemd[951]: roboticscape.service: Failed at step EXEC spawning /etc/roboticscape/link_to_startup_program: No such file or directory

Signed-off-by: Robert Nelson <robertcnelson@gmail.com>

Just exit cleanly when rc_model doesn't match grep of /boot/uEnv.txt

Fixes:
sudo systemctl restart roboticscape
Job for roboticscape.service failed because the control process exited with error code.
See "systemctl status roboticscape.service" and "journalctl -xe" for details.

systemd[1]: Starting roboticscape...
rc_startup_routine[867]: roboticscape service can only run on BB Blue, Black, and Black wireless when the roboticscape device tree is in use.
systemd[1]: roboticscape.service: Control process exited, code=exited status=255
systemd[1]: roboticscape.service: Failed with result 'exit-code'.
systemd[1]: Failed to start roboticscape.

Signed-off-by: Robert Nelson <robertcnelson@gmail.com>

all math libs in double-precision floats now due to rounding errors causing unstable transfer functions