optimizing check_forked check if -u is supported

[elreydetoda]

even when running in the noerror mode (i.e. set -e) you shouldn't have to unset and check for the exit status, but instead the if statement should handle the error and continue normally if it exists (-u does exist) and it will exit with a 0, or in this case not go into the if statement at all (since you don't have an else statement) if it fails.