Bug#12845 - Stress test: Server crashes on CREATE .. SELECT statement

Solution for 4.0 and 4.1.
If the caller cannot re-open table(s), it gives a NULL
'refresh' argument to open_table(). We used to ignore
flushes then. Now we ignore drops too.

sql/sql_base.cc

@@ -871,6 +871,13 @@ TABLE *open_table(THD *thd,const char *db,const char *table_name,
   {
     if (table->version != refresh_version)
     {
+      if (! refresh)
+      {
+        /* Ignore flush for now, but force close after usage. */
+        thd->version= table->version;
+        continue;
+      }
+
       /*
       ** There is a refresh in progress for this table
       ** Wait until the table is freed or the thread is killed.