Port the Facebook patch for releasing InnoDB row locks early to the
MWL#116 framework.

A new --innodb-release-locks-early option (off by default) enables a
prepare_ordered() handlerton method which will release row locks and
commit a transaction to memory immediately after successful prepare.

If the server subsequently tries to rollback (ie. due to binlog error),
crashes the server to prevent corrupting the InnoDB state.

mysql-test/r/innodb_release_row_locks_early.result:
  Test case.
mysql-test/t/innodb_release_row_locks_early-master.opt:
  Test case.
mysql-test/t/innodb_release_row_locks_early.test:
  Test case.
sql/log.cc:
  Add DEBUG_SYNC points for testing.
storage/xtradb/handler/ha_innodb.cc:
  Release locks during prepare phase if --innodb-release-locks-early.
  Crash the server if we are asked to rollback after releasing locks and
  committing the transaction to memory.
storage/xtradb/include/srv0srv.h:
  Add variable for --innodb-release-locks-early option.
storage/xtradb/include/trx0sys.ic:
  If --innodb-release-locks-early, treat a transaction as committed to memory
  as soon as it enters the TRX_PREPARED state.
storage/xtradb/srv/srv0srv.c:
  Add variable for --innodb-release-locks-early option.