Let InnoDB use a consistent read when it initializes the auto-inc counter for a table: this will eliminate spurious deadlocks, but will ignore an UPDATE if that happens at the same time that we init the auto-inc counter; this has to be documented; this path also fixes most of Bug #11633, but not all: if ::external_lock() is not called on the table in SHOW TABLE STATUS, that might cause a crash if someone simultaneously DROPs the table