Implement IRC-style case equivalence

[progval]

RFC 1459 and RFC 2812:

Because of IRC's scandanavian origin, the characters {}| are
considered to be the lower case equivalents of the characters [],
respectively.

Charybdis and InspIRCd respect this, but not Mammon.

[DanielOaks]

That applies for CASEMAPPING=rfc1459.

We use the proposed RPL_ISUPPORT token value CASEMAPPING=rfc3454, described here, which we think is more suitable for software these days. This is because it defines a more extensive casemapping which works nicely with UTF-8.

This is not a bug, as we clearly define this with our CASEMAPPING RPL_ISUPPORT token. The same should go for Charybdis and InspIRCd, which should present something along the lines of: CASEMAPPING=rfc1459 or similar describing their adherence to this.

[progval]

Fair enough