Comment 2 for bug 1260193

If the parameter is set at runtime, Galera returns 'Unknown
parameter' to stderr and also "ERROR 1210 (HY000): Incorrect
arguments to SET" to client.

However, this checking is not done at init.

wsrep_set_params called in galera_init has checking for unknown
parameters. However,

galera::ReplicatorSMM::param_set:

    try
    {
        if (config_.get(key) == value) return;
    }
    catch (gu::NotFound&) {}

applies to all provided options (even base_host). So, rest of the
function is bypassed.

This is because they (the config_ map) are initialised earlier in
gu::Config::parse where there is no checking of keys.