HostServ: ident@host vhosts (CHGIDENT)

A vhost may be ident@host, not just host: apply_vhost splits it and sends
CHGIDENT for the ident plus CHGHOST for the host. valid_vhost validates
the optional ident part; ON/SET/ACTIVATE/identify all route through
apply_vhost, so a bare host still works unchanged. New SetIdent action.

nickserv/src/identify.rs

@@ -61,7 +61,7 @@ pub fn handle(me: &str, from: &Sender, args: &[&str], ctx: &mut ServiceCtx, db:
             }
             // Apply the account's vhost (HostServ), if it has one.
             if let Some(v) = db.vhost(&account) {
-                ctx.set_host(from.uid, &v.host);
+                ctx.apply_vhost(from.uid, &v.host);
             }
             // Let them know about waiting memos.
             let unread = db.unread_memos(&account);