Fixes the following bugs:

Bug #30706: SQL thread on slave is allowed to block client queries when slave load is high
  Add (innodb|innobase|srv)_replication_delay MySQL config parameter.

Bug #30888: Innodb table + stored procedure + row deletion = server crash
  While adding code for the low level read of the AUTOINC value from the index,
  the case for MEDIUM ints which are 3 bytes was missed triggering an
  assertion.

Bug #30907: Regression: "--innodb_autoinc_lock_mode=0" (off) not same as older releases
  We don't rely on *first_value to be 0 when checking whether
  get_auto_increment() has been invoked for the first time in a multi-row
  INSERT. We instead use trx_t::n_autoinc_rows. Initialize trx::n_autoinc_rows
  inside ha_innobase::start_stmt() too.

Bug #31444: "InnoDB: Error: MySQL is freeing a thd" in innodb_mysql.test
  ha_innobase::external_lock(): Update prebuilt->mysql_has_locked and
  trx->n_mysql_tables_in_use only after row_lock_table_for_mysql() returns
  DB_SUCCESS.  A timeout on LOCK TABLES would lead to an inconsistent state,
  which would cause trx_free() to print a warning.

Bug #31494: innodb + 5.1 + read committed crash, assertion
  Set an error code when a deadlock occurs in semi-consistent read.