External strings

Strings can use external buffers to store their contents.

lgc.c

@@ -813,7 +813,9 @@ static void freeobj (lua_State *L, GCObject *o) {
     }
     case LUA_VLNGSTR: {
       TString *ts = gco2ts(o);
-      luaM_freemem(L, ts, sizestrlng(ts->u.lnglen));
+      if (ts->shrlen == LSTRMEM)  /* must free external string? */
+        (*ts->falloc)(ts->ud, ts->contents, ts->u.lnglen + 1, 0);
+      luaM_freemem(L, ts, luaS_sizelngstr(ts->u.lnglen, ts->shrlen));
       break;
     }
     default: lua_assert(0);