0. Enable email verification
1. Register `dog`
2. Register `d0g`
3. Verify `dog`
4. Verify `d0g`: verification succeeds but the nick cannot be used

This affects RPL_WHOISACTUALLY and possibly others.

1. Avoid undefined behavior of time.Time{}.UnixNano()
2. Times should be compared with Equal()

ParseUserModeChanges and ParseChannelModeChanges already validate
that the modes are modifiable, so there's no need to repeat it here.

thanks @ajaspers!

Add chanmode preventing speech to error message.

Fixes #1182.

CLIENTS LIST shows information about clients attached to a nick.
CLIENTS LOGOUT allows individual (or all) sessions to be logged out.

SESSIONS is now an alias for CLIENTS LIST.

Fixes #1072.

See #1240.

anything other than a (net.Error) with Temporary() == true
is treated as a fatal error that causes the http server to exit

See discussion on #68.