Use the warn(3) functions instead of fprintf(3).

Use the warn(3) functions instead of fprintf(3).

Rather than using fprintf(3) to display a formatted error message on
stderr (and, occasionally in conjunction with strerror(3)), use the
warn(3) functions. A few cases that also used perror(3) were changed
accordingly, as well.

While there, remove an extra fprintf(3) call in conf_load which is
already followed by an err(3).

ok marco