recovered transactions from new ones.  Until r1594, they were distinguished
by trx->sess == NULL.

trx_t: Add the bitfield is_recovered.

trx_lists_init_at_db_start(): Set trx->is_recovered.

trx_create(): Initialize trx->is_recovered = 0.

trx_print(): Display information about trx->is_recovered.

trx_rollback_or_clean_all_without_sess(): Skip new transactions.
Protect all accesses of trx_sys->trx_list with kernel_mutex.

trx_roll_crash_recv_trx, trx_roll_max_undo_no, trx_roll_progress_printed_pct:
Made these variables static.