Add support for CIDR wildcard masks so that domain ranges can be provided

[jhubert]

A network may have a specific domain range that it wants to whitelist. Instead of specifying all or none (ie: n or *), it would great if they could use the CIDR standard to define their range.

For example 192.168.0.1/24 would allow all 192.168.0.* addresses, but 192.168.0.0/30 would only match 192.168.0.[0-3].

The NetAddr gem has a CIDR class the provides a simple matches? method to handle the comparison. This would also have the added benefit of supporting IPv6 addresses.