It doesn't match Dovecot convention.

It can't be done anymore by modifying settings directly.

Also change the callers to not bother storing it separately. Instead, they
can just use mail_user_r->service_user.

Adds status parameter to sieve_result_execute().

Providing an out-of-range index caused an assert panic.

Panic was:

Panic: file mail-index-transaction-update.c: line 19 (mail_index_transaction_lookup): assertion failed: (seq >= t->first_new_seq && seq <= t->last_new_seq)