upstream commit

Validate address ranges for AllowUser/DenyUsers at
configuration load time and refuse to accept bad ones. It was previously
possible to specify invalid CIDR address ranges (e.g. djm@127.1.2.3/55) and
these would always match.

Thanks to Laurence Parry for a detailed bug report. ok markus (for
a previous diff version)

Upstream-ID: 9dfcdd9672b06e65233ea4434c38226680d40bfb
