We didn't expect "error: no error", although this is
in fact a legitimate state (if something is erroneous
on the master, but not on the slave, e.g. INSERT fails
on master due to UNIQUE constraint which does not exist
on slave).
We now list the ignore for "0: no error" the same way
as any other ignore; moreover, if no or an empty
--slave-skip-errors is passed at start-up, we show
"OFF" instead of empty list, as intended. (The code
for that was there, but was only run for the empty-
argument case, even if it subsequently tested for
both conditions.)
