Use method indices as LuaLuna thunk upvalues

Rather than member function pointers, which are not necessarily simple pointers and are not necessarily convertible to void * sensibly. This also gets rid of the last instance of lua_pushlightuserdata, which apparently isn't super well-supported by luajit, and which thus often crash on android.

src/lua/LuaLuna.h

@@ -57,7 +57,7 @@ public:
 		{
 			/* edited by Snaily: shouldn't it be const RegType *l ... ? */
 			lua_pushstring(L, l->name);
-			lua_pushlightuserdata(L, (void*)l);
+			lua_pushinteger(L, l - T::methods);
 			lua_pushcclosure(L, thunk, 1);
 			lua_settable(L, methods);
 		}
@@ -116,7 +116,7 @@ private:
 		T *obj = check(L, 1);  // get 'self', or if you prefer, 'this'
 		lua_remove(L, 1);  // remove self so member function args start at index 1
 		// get member function from upvalue
-		RegType *l = static_cast<RegType*>(lua_touserdata(L, lua_upvalueindex(1)));
+		RegType *l = T::methods + lua_tointeger(L, lua_upvalueindex(1));
 		return (obj->*(l->mfunc))(L);  // call member function
 	}