add sp (script password) to LOGIN compat flags
switch to new BATTLEOPENED message (compat flag eb changed to cl)
send EXIT message on disconnect
silently ignore empty sentences

I got tired of seeing the warnings, but i still think its silly that uberserver consider it ok to send empty sentences, e.g. "MOTD ".
Now also using istream::eof() instead of relying on exception to see if stream extraction is complete.