Fix the signal handler.

The signal handler was always fishy since it modified the global process
state but worked on all common platforms. libcurl turns the process into
a multithreaded environment, thus breaking that fragile construction.
After the signal handler was called the global state is inconsistent and
there's a high chance of things going wrong. For example at the net curl
download or when setjmp() is called in Qcommon_Frame().

src/backends/unix/signalhandler.c

@@ -118,10 +118,12 @@ signalhandler(int sig)
 	raise(sig);
 }
 
+extern qboolean quitnextframe;
+
 void
 terminate(int sig)
 {
-	Cbuf_AddText("quit");
+	quitnextframe = true;
 }
 
 void

src/common/frame.c

@@ -76,6 +76,10 @@ qboolean is_portable;
 // Game given by user
 char userGivenGame[MAX_QPATH];
 
+// Game should quit next frame.
+// Hack for the signal handlers.
+qboolean quitnextframe;
+
 // ----
 
 static void
@@ -424,6 +428,14 @@ Qcommon_Frame(int msec)
 	static qboolean last_was_packetframe;
 
 
+	/* Tells the client to shutdown.
+	   Used by the signal handlers. */
+	if (quitnextframe)
+	{
+		Cbuf_AddText("quit");
+	}
+
+
 	/* In case of ERR_DROP we're jumping here. Don't know
 	   if that' really save but it seems to work. So leave
 	   it alone. */
@@ -731,6 +743,14 @@ Qcommon_Frame(int msec)
 	qboolean packetframe = true;
 
 
+	/* Tells the client to shutdown.
+	   Used by the signal handlers. */
+	if (quitnextframe)
+	{
+		Cbuf_AddText("quit");
+	}
+
+
 	/* In case of ERR_DROP we're jumping here. Don't know
 	   if that' really save but it seems to work. So leave
 	   it alone. */