addmultisigaddress creates an address respecting the setting, being unable to generate a specific type of address without also adding it to the wallet seems wrong.

I suppose in the future `addresstype` may be refactored to be wallet-specific, which would leave this non-wallet rpc call without an argument. Perhaps there should just be an optional parameter to set it.
{
    if (request.fHelp || request.params.size() != 2)
        throw std::runtime_error(
            "signmessagewithprivkey \"privkey\" \"message\"\n"
            "\nSign a message with the private key of an address\n"
            "\nArguments:\n"
            "1. \"privkey\"         (string, required) The private key to sign the message with.\n"
            "2. \"message\"         (string, required) The message to create a signature of.\n"
            "\nResult:\n"
            "\"signature\"          (string) The signature of the message encoded in base 64\n"
            "\nExamples:\n"
            "\nCreate the signature\n"
            + HelpExampleCli("signmessagewithprivkey", "\"privkey\" \"my message\"") +
            "\nVerify the signature\n"
            + HelpExampleCli("verifymessage", "\"1D1ZrZNe3JUo7ZycKEYQQiQAWd9y54F4XX\" \"signature\" \"my message\"") +
            "\nAs json rpc\n"
            + HelpExampleRpc("signmessagewithprivkey", "\"privkey\", \"my message\"")
        );
    std::string strPrivkey = request.params[0].get_str();
    std::string strMessage = request.params[1].get_str();
    CKey key = DecodeSecret(strPrivkey);
    if (!key.IsValid()) {
        throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, "Invalid private key");
    }
    CHashWriter ss(SER_GETHASH, 0);