Because this API only errors when write!() errors occur, we can return
the exit code as an error here.
This way the user of the API can immediately exit if there was an IO
error, but the API automatically takes care of the right return value,
returning (exiting) with zero (0) if there was an "Broken pipe" error
and with one (1) otherwise, which is the expected behaviour here.
All calls to that API were changed accordingly.
Signed-off-by: Matthias Beyer <mail@beyermatthias.de>
