trx_state_eq(): Add the parameter bool relaxed=false, to
allow trx->state==TRX_STATE_NOT_STARTED where a different
state is expected, if an error has been reported.

trx_release_savepoint_for_mysql(): Pass relaxed=true to
trx_state_eq(). That is, allow the transaction to be idle
when ROLLBACK TO SAVEPOINT is attempted after an error
has been reported to the client.