Avoid overflows when incrementing parameters in C

Any C function can receive maxinteger as an integer argument, and
therefore cannot increment it without some care (e.g., doing unsigned
arithmetic as the core does).

lauxlib.h

@@ -154,6 +154,14 @@ LUALIB_API void (luaL_requiref) (lua_State *L, const char *modname,
 #define luaL_loadbuffer(L,s,sz,n)	luaL_loadbufferx(L,s,sz,n,NULL)
 
 
+/*
+** Perform arithmetic operations on lua_Integer values with wrap-around
+** semantics, as the Lua core does.
+*/
+#define luaL_intop(op,v1,v2)  \
+	((lua_Integer)((lua_Unsigned)(v1) op (lua_Unsigned)(v2)))
+
+
 /* push the value used to represent failure/error */
 #define luaL_pushfail(L)	lua_pushnil(L)