Only display stacktraces in a window on Windows platform (#772)

hxd/System.hl.hx

@@ -158,7 +158,11 @@ class System {
 		#if usesys
 		haxe.System.reportError(err + stack);
 		#else
-		Sys.println(err + stack);
+		Sys.stderr().writeString(err + stack + "\n");
+
+		if ( Sys.systemName() != 'Windows' )
+			return;
+
 		if( dismissErrors )
 			return;