retro compatible with Lua 5.1 C/API

Signed-off-by: Francois Perrad <francois.perrad@gadz.org>

Index: b/lbase64.c
===================================================================
--- a/lbase64.c
+++ b/lbase64.c
@@ -111,7 +111,11 @@
 
 LUALIB_API int luaopen_base64(lua_State *L)
 {
+#if LUA_VERSION_NUM >= 502
  luaL_newlib(L,R);
+#else
+ luaL_register(L,MYNAME,R);
+#endif
  lua_pushliteral(L,"version");			/** version */
  lua_pushliteral(L,MYVERSION);
  lua_settable(L,-3);