Fix Lua examples for running under Lua 5.2

Includes cherry picking parts of
ce2760f77e

Examples/lua/embed3/embed3.cpp

@@ -26,11 +26,15 @@ extern "C" {
 #include <lauxlib.h>
 #include <lualib.h>
 }
-
-/* The SWIG external runtime is generated by using.
-swig -lua -externalruntime swigluarun.h
-It contains useful function used by SWIG in its wrappering
-SWIG_TypeQuery() SWIG_NewPointerObj()
+
+#if LUA_VERSION_NUM > 501
+#define lua_open luaL_newstate
+#endif
+
+/* The SWIG external runtime is generated by using.
+swig -lua -externalruntime swigluarun.h
+It contains useful function used by SWIG in its wrappering
+SWIG_TypeQuery() SWIG_NewPointerObj()
 */
 #include "swigluarun.h"   // the SWIG external runtime
 
@@ -65,8 +69,7 @@ int call_onEvent(lua_State *L, Event e) {
   push a, push b, call 'add' check & return res
   */
   top = lua_gettop(L);  /* for later */
-  lua_pushstring(L, "onEvent");                                  /* function name */
-  lua_gettable(L, LUA_GLOBALSINDEX);               /* function to be called */
+  lua_getglobal(L, "onEvent");               /* function to be called */
   if (!lua_isfunction(L, -1)) {
     printf("[C++] error: cannot find function 'OnEvent'\n");
     lua_settop(L, top);  // reset