occur in mysql-test-run, but mysql-test-run reports some warnings for
some tests and incorrect results for innodb-index.test.

innobase_start_trx_and_assign_read_view(): Use thd instead of current_thd.

ha_innobase::add_index(): Use ha_thd() instead of current_thd.
Commit the transaction at the end.

row_merge_rename_index(): Really change the name of the index.  This was
broken in r1430.