postToMap.sh: Implement --force
postToMap.sh: Implement --force

* Implement "--force" to force an update - useful if it's the wrong day.
* Disabled some shellcheck errors.
* Save the full output from curl for use in error messages.
* Check for null reply from server.
thomasjacquin/allsky,thomasjacquin/allsky,thomasjacquin/allsky