Added snotes for failed SASL authentication attempts if need_sasl flag is set

Many thanks to Shockk for this patch.

References commits:
 - 15dc12b76e76c6fa2ead773b6b40965223ad453f - Added snotes for failed SASL authentication attempts if need_sasl flag is set.
 - febd2e2aca27f7f1acfc522f3fda65d8be067edc - Updated help/opers/snomask to add +S snomask.
Merge branch 'failed-sasl-snomask' into devel