Clearer distinction between types and tags

LUA_T* represents only types; tags (types + Variants) are represented
by LUA_V* constants.

liolib.c

@@ -215,7 +215,7 @@ static int f_close (lua_State *L) {
 
 static int io_close (lua_State *L) {
   if (lua_isnone(L, 1))  /* no argument? */
-    lua_getfield(L, LUA_REGISTRYINDEX, IO_OUTPUT);  /* use standard output */
+    lua_getfield(L, LUA_REGISTRYINDEX, IO_OUTPUT);  /* use default output */
   return f_close(L);
 }
 
@@ -296,7 +296,7 @@ static FILE *getiofile (lua_State *L, const char *findex) {
   lua_getfield(L, LUA_REGISTRYINDEX, findex);
   p = (LStream *)lua_touserdata(L, -1);
   if (isclosed(p))
-    luaL_error(L, "standard %s file is closed", findex + IOPREF_LEN);
+    luaL_error(L, "default %s file is closed", findex + IOPREF_LEN);
   return p->f;
 }