Added semi-workaround method for network thread shutdown:

Currently closing game while network thread is waiting for something is
very bug-prone, since network thread may resume during shutdown and
access partially destroyed client state.

Now if exit has been requested, the very first step would be semi-
graceful shutdown of network thread (via exception throwing). This may
in theory skip some cleanup in non-RAII code, but since game is shutting
down this does not matters much.

This logic applies to:
- shutting down while network thread is waiting for dialogs
- shuttind down while network thread waiting for animations in combat

client/mainmenu/CMainMenu.cpp

@@ -58,7 +58,7 @@
 #include "../../lib/CConfigHandler.h"
 #include "../../lib/GameConstants.h"
 #include "../../lib/CRandomGenerator.h"
-#include "../../lib/CondSh.h"
+#include "../ConditionalWait.h"
 
 std::shared_ptr<CMainMenu> CMM;
 ISelectionScreenInfo * SEL;