After an ignored INSERT IGNORE statement into an empty table, we would
wrongly use the MDEV-515 table-level undo logging for a subsequent
REPLACE statement.

ha_innobase::reset_template(): Clear m_prebuilt->ins_node->bulk_insert
on every statement boundary.

ha_innobase::start_stmt(): Invoke end_bulk_insert().

ha_innobase::extra(): Avoid accessing m_prebuilt->trx. Do not call
thd_to_trx(). Invoke end_bulk_insert() and try to reset bulk_insert
when changing the REPLACE or IGNORE settings.

trx_mod_table_time_t::WAS_BULK: Use a distinct value from BULK.

trx_undo_report_row_operation(): Add debug assertions.

Note: Some calls to end_bulk_insert() may be redundant, but statement
boundaries are not always clear in the API (especially in the
presence of LOCK TABLES or stored procedures).