Change IAC + GA to key off of MUDPROMPT @option

Several clients interpret IAC + GA as a linefeed, in order
to support MUDs that always end a line with them.  This causes
Evennia to spew empty lines everywhere if IAC + GA is always on.

evennia/server/inputfuncs.py

@@ -193,7 +193,8 @@ def client_options(session, *args, **kwargs):
                            "UTF-8", "SCREENREADER", "ENCODING",
                            "MCCP", "SCREENHEIGHT",
                            "SCREENWIDTH", "INPUTDEBUG",
-                           "RAW", "NOCOLOR"))
+                           "RAW", "NOCOLOR",
+                           "MUDPROMPT"))
         session.msg(client_options=options)
         return
 

evennia/server/portal/telnet.py

@@ -221,7 +221,9 @@ class TelnetProtocol(Telnet, StatefulTelnetProtocol, Session):
         # escape IAC in line mode, and correctly add \r\n
         line += self.delimiter
         line = line.replace(IAC, IAC + IAC).replace('\n', '\r\n')
-        return self.transport.write(mccp_compress(self, line + IAC + GA))
+        if self.protocol_flags.get("MUDPROMPT", False):
+            line = line + IAC + GA
+        return self.transport.write(mccp_compress(self, line))
 
     # Session hooks