added check for conversion 'obj2gco' (and corrections for small

problems detected by this check)

lstring.c

@@ -1,5 +1,5 @@
 /*
-** $Id: lstring.c,v 2.39 2014/04/02 16:44:42 roberto Exp roberto $
+** $Id: lstring.c,v 2.40 2014/06/18 22:59:29 roberto Exp roberto $
 ** String table (keeps all strings handled by Lua)
 ** See Copyright Notice in lua.h
 */
@@ -126,8 +126,8 @@ static TString *internshrstr (lua_State *L, const char *str, size_t l) {
     if (l == ts->tsv.len &&
         (memcmp(str, getstr(ts), l * sizeof(char)) == 0)) {
       /* found! */
-      if (isdead(g, obj2gco(ts)))  /* dead (but not collected yet)? */
-        changewhite(obj2gco(ts));  /* resurrect it */
+      if (isdead(g, ts2gco(ts)))  /* dead (but not collected yet)? */
+        changewhite(ts2gco(ts));  /* resurrect it */
       return ts;
     }
   }