#245 use row estimate parameter to start_bulk_insert to decide if a loader is used

storage/tokudb/ha_tokudb.cc

@@ -3250,7 +3250,7 @@ void ha_tokudb::start_bulk_insert(ha_rows rows) {
     num_DBs_locked_in_bulk = true;
     lock_count = 0;
     
-    if (share->try_table_lock) {
+    if ((rows == 0 || rows > 1) && share->try_table_lock) {
         if (get_prelock_empty(thd) && may_table_be_empty(transaction)) {
             if (using_ignore || is_insert_ignore(thd) || thd->lex->duplicates != DUP_ERROR) {
                 acquire_table_lock(transaction, lock_write);