Discard old server commands upon new gamestate

Fixes Unvanquished/Unvanquished#1102.

This fixes a bug where the configstring state could be wrong due to `cs`
server commands being executed out of order with respect to game state
processing. Server commands are only processed when the cgame requests a
snapshot, so commands received before the client loads the current map
which were sent before the gamestate could be processed after the
gamestate.

Of course there are other commands besides setting configstrings. In
general, processing a command from a previous game seems very likely to
be a bad idea and unlikely to be good.

Author: slipher

src/engine/client/cl_parse.cpp

@@ -409,6 +409,9 @@ void CL_ParseGamestate( msg_t *msg )
 
 		// a gamestate always marks a server command sequence
 		clc.serverCommandSequence = MSG_ReadLong( msg );
+
+		// trash any commands from previous game
+		clc.lastExecutedServerCommand = clc.serverCommandSequence;
 	}
 
 	// parse all the configstrings and baselines

src/engine/server/sv_client.cpp

@@ -354,6 +354,7 @@ void SV_SendClientGameState( client_t *client )
 	// we have to do this cause we send the client->reliableSequence
 	// with a gamestate and it sets the clc.serverCommandSequence at
 	// the client side
+	// TODO(0.57): remove. The client will just throw away old commands on getting a gamestate
 	SV_UpdateServerCommandsToClient( client, &msg );
 
 	// send the gamestate