Bug #16979: AUTO_INC lock in InnoDB works a table level lock
  Add a table level counter that tracks the number of AUTOINC locks that are
  pending and/or granted on a table. We peek at this value to determine whether
  a transaction doing a simple INSERT in innodb_autoinc_lock_mode = 1, needs to
  acquire the AUTOINC lock or not. This change is related to Bug# 16979.
Bug #27950: Duplicate entry error in auto-inc after mysqld restart
  We check whether the AUTOINC sub-system has been initialized (first) by
  holding the AUTOINC mutex and if initialization is required then we
  initialize using our normal procedure.