Fix stack balancing problems by refactoring execution calls

- Con::executef now uses a template
- All public execution functions now restore the console stack upon return
- Fixed bad parameters on some callbacks
- Reverts get*Arg behavior

Engine/source/sim/netDownload.cpp

@@ -23,6 +23,7 @@
 #include "platform/platform.h"
 #include "core/dnet.h"
 #include "console/simBase.h"
+#include "console/engineAPI.h"
 #include "sim/netConnection.h"
 #include "core/stream/bitStream.h"
 #include "core/stream/fileStream.h"