Changed the protocol for VoIP packets to support legacy clients.

Previously, a legacy client wouldn't get a VoIP packet, but if they did,
 they'd panic and disconnect. Now they ignore them and continue on. This also
 gives us the framework to add other features legacy clients can ignore.

Oh, this also has the benefit of allowing us to store incoming VoIP for
 playback in recorded demos. They'll play the chatter on VoIP clients, and
 be ignored on legacy ones. Huge win.

code/client/cl_input.c

@@ -760,6 +760,8 @@ void CL_WritePacket( void ) {
 
 	#if USE_VOIP
 	if (clc.voipOutgoingDataSize > 0) {  // only send if data.
+		MSG_WriteByte (&buf, clc_EOF);  // placate legacy servers.
+		MSG_WriteByte (&buf, clc_extension);
 		MSG_WriteByte (&buf, clc_voip);
 		MSG_WriteByte (&buf, clc.voipOutgoingGeneration);
 		MSG_WriteLong (&buf, clc.voipOutgoingSequence);