Fix for bug #29980: 5.1.20 ate my table

Problem: trying to repair an old (e.g. with "old" varstring fields) corrupted 
table with use_frm option we don't actually repair the table, just altering it
which may couse data loss.

Fix: if use_frm repair option is set, do repair instead of altering even 
if the table needs upgrade.

sql/sql_table.cc

@@ -4132,7 +4132,8 @@ static bool mysql_admin_table(THD* thd, TABLE_LIST* tables,
         goto err;
     }
 
-    if (operator_func == &handler::ha_repair)
+    if (operator_func == &handler::ha_repair &&
+        !(check_opt->sql_flags & TT_USEFRM))
     {
       if ((table->table->file->check_old_types() == HA_ADMIN_NEEDS_ALTER) ||
           (table->table->file->ha_check_for_upgrade(check_opt) ==