Fixed flush table issue in MyISAM with CREATE ... SELECT

When doing CREATE TABLE ... ENGINE=MyISAM SELECT ...
the MyISAM table was not completely flushed at commit
which gave some warnings about table not closed in the
atomic test suite.

Fixed by flushing the table in select_insert::prepare_eof().

Author: montywi

storage/myisam/mi_extra.c

@@ -282,6 +282,7 @@ int mi_extra(MI_INFO *info, enum ha_extra_function function, void *extra_arg)
     mysql_mutex_unlock(&share->intern_lock);
     mysql_mutex_unlock(&THR_LOCK_myisam);
     break;
+  case HA_EXTRA_END_ALTER_COPY:
   case HA_EXTRA_FLUSH:
     if (!share->temporary)
       flush_key_blocks(share->key_cache, share->kfile, &share->dirty_part_map,