parse: minimum options values are signed

parse: minimum options values are signed

Rebecca reports that using an invalid value for the nice
parameter yields:

min value out of range: 18446744073709551596 (4294967277 min)

where it really should be:

min value out of range: -20 (-19 min)

Print the minimum values as signed, if we hit the out-of-range
error.

Signed-off-by: Jens Axboe <axboe@kernel.dk>