add # to disfavoredNameCharacters

Partially fixes #1679, not sure whether to police the relaymsg config or not

irc/strings.go

 	// #1436: we discovered that these characters are problematic,
 	// so we're disallowing them in new nicks/account names, but allowing
 	// previously registered names
-	disfavoredNameCharacters = `<>'";`
+	disfavoredNameCharacters = `<>'";#`
 )
 
 var (